What are the active player factions on this server these days? Wanting to join one
The Red Briar is active, lacking members currently.
Violet Flame is active too. Velethuil is also active,
and so are the Purple Dragons.
It really depends what kind of character you want to play.
A faction with a lot of members in it preferably
The sad reality is that currently the player factions on the server are by and large all desperately in need of more active players. The Briar, Velethuil, and the Violet Flame are among the most active, but even amongst them you can really only count on between 2 and 4 players to regularly log in characters from any of these factions. The Arabel Council is another faction with about the same number regularly active if you're into the political scene.
There have been many more factions on the server that have been active in the past - all founded by players. Among them:
Harpers
Hullack Druid Circle
Sharan Cell
However, so far as I know with these (with the exception of the Harpers) there is little activity these days.
My recommendation if you're seeking a player faction with a large following is to found your own and rally people to your cause. Part of why the factions of old are suffering right now is many of their players have left or become too busy irl to devote much time to the game, so it makes more sense to found a faction with players who you see on every day. That said, it's likely getting your hopes up a bit too much to expect more than 4 or 5 regularly active characters in any faction given the size of the server. You have to consider that 4 or 5 is roughly a fifth to a quarter of the players logged onto the server at any given time - sometimes more.
Alternatively, for those belonging to factions reading this it would seem like it's a good idea to break out those characters and start seeking recruits for a revival. Not to plug myself, but one of my characters is actually founding a faction to help him establish a new city. I've had limited time on lately, but his plans are pretty much public knowledge and he's personally invited a few people to join him in the endeavor. I'm always looking for those interested in lending a hand with it both IC and OOC though, if you think that's something your character would want to be a part of. Still, above all else I think now is the perfect time for players to found new factions. The server's on a sort of upswing of new players joining, so there's likely to be a large amount of them within the same level range actively playing and thus plenty to back you up on your endeavors.
As always, feel free to request assistance from myself or other DMs in terms of events and what-not to help establish these factions. I hope this offers some insight for you, and if you still want to join an established faction on the server ask around about the names listed above and eventually you'll be guided to someone who can get you in. Remember: those factions are as hungry for new recruits as you are to join them.

We also have a Drow house that is fairly active if you are interested in a trying a Drow PC.
or ! You could join the growing circle that is the temple of Oghma!
All glory to Oghma

Cormyrian book club is go! Oghma 4 lyfe
Harpers, as mentioned are active(ish), though obviously fairly secretive. Feel free to PM me about them if that's the angle you want to go with.
We're going to be trying to get more people involved with the council in the next few weeks (might end up being mid-May), if you're of a political bend as was also mentioned.
In general, there are a lot of characters in various factions, but not all of those factions are actively doing things as a faction. Usually what makes them more active is when other people want to do stuff, or bring up the faction, or organize things - even just little trips to dungeons and such.
CD is very much about taking initiative and shaping the world as you want to shape it, whether that means stepping up to take charge of an existing group or faction, or starting your own with a few like minded individuals.
Since this is was brought up, would there happen to be any rogue guilds around or active?
Depends what you mean by "rogue guild". I don't think we have any active thieves' guilds or similar shady underground groups, if that's what you mean.
The majority of groups, pretty much just excluding the local Druids' Grove and the Violet Flame (the resident academy of the arcane), are less oriented around classes and more around alignments, religions, residency, mutual goals or intents, or in-character friendships and alliances.
It's hard to peg down what kind of factions and guilds people would be interested in from the perspective of simply naming a class, when almost every group on the server is far more interested in what you want and what you believe than in what tools you use to accomplish it.
So the questions for you and anyone else looking for a group or organization to attach themselves to should probably be more along the lines of "What does my character want?", "Who am I interested in working with?", "What am I willing to cooperate with and what measures am I willing to take to reach my goals?", "What ethical or moral lines to I draw and why?", and those sorts of things. Answering those will be far more likely to point you in the direction of a guild or faction you can fit into well.
Since this is was brought up, would there happen to be any rogue guilds around or active?
I don't know if a thieves guild exists but I have recently been considering making a quest request that might help establish one, since the big problem I would imagine with such a guild would be well, folks getting together to form it icly.
A thieves' guild would really require a DM or two to be fairly attentive and open and available for people to contact, possibly with some kind of Godfather-like NPC who would send his/her minions to recruit promising PCs with the right mindsets and array of skills. The trick, of course, is finding the DMs to do so.
There's the alternative method of player-operated guilds of such sort, of course, but those are a little more difficult to arrange and come with a much larger risk of someone spilling the beans to the server public.
There were one or two rogue-type guilds that were semi-active, but I believe both have since folded due to either lack of interest or player rl activities. Clockwork Security was the big one, there. They offered security services, had a bank (that I think was more rp-oriented and didn't actually have 'real' money stored in it).
Since this is was brought up, would there happen to be any rogue guilds around or active?
I don't know if a thieves guild exists but I have recently been considering making a quest request that might help establish one, since the big problem I would imagine with such a guild would be well, folks getting together to form it icly.
For those interested in establishing a thieves guild, please -do- make a quest request or PM myself or another staff member to let us know your interest. I will endeavor to oversee as many of these as I can. It would help, though, if you include the names of all those interested in assisting with such. I would ask that any quest request for establishing a faction have at least 5 interested parties willing to contribute to the founding of such.
Was pondering starting something with Bela, but still rolling around a whole lot of different things in my head about that particular front. There really aren't too many rogue-ish types around compared to other choices. If you need an extra head for it, Darvins, lemmie know. (Though Bela dislikes thieves intently, even so!)
~BR
I also have a character not adverse to underhandedness if you still want to do something Darvins. Actually, I have two

Depends what you mean by "rogue guild".
I wasn't specifically narrowing it down to a class guild. I guess it was badly worded. I was asking about morally-shady, criminally minded factions.
A thieves' guild would really require a DM or two to be fairly attentive and open and available for people to contact, possibly with some kind of Godfather-like NPC who would send his/her minions to recruit promising PCs with the right mindsets and array of skills. The trick, of course, is finding the DMs to do so.
This was my concern in asking. This type of guild isn't something that is easy to assemble, plus if someone just starts a guild in the middle of someone's turf, it usually doesn't end well. So I was just checking.
I don't know if a thieves guild exists but I have recently been considering making a quest request that might help establish one, since the big problem I would imagine with such a guild would be well, folks getting together to form it icly.
This is true, its hard to assemble shady types. Ultimately, I was just looking for a place where my character could get some training in techniques etc.
I think a big question on such a thing, through I will make the quest request if there is interest either way, just affects if my own char would join said guild, is do people want a CN-CG Guild or a CN-CE guild, because the two are very different. A CG-CN guild is smuggling, theft yes but skill thefts more often, while a CE-CN Guild would be more about the fear and protection moneys and the such I think. ((My Char would be more a CG-CN type person)) but the request itself would be for some sort of big heist where folks where recruited by an outside element, someone like Brad works well as the fixer, then afterwards those interested could happily form a guild based on feeling they have similar views.
My character is actually NE, but honestly would be fine with the smuggling, in fact awhile back I was trying to establish something along those lines with another DM but i never followed up and I don't think they are around anymore. We may just have to gather interested players together oocly and have a discussion about where our interests lay.
You could also have LE characters in a theives guild. Lawful doesn't mean "following the law of the land", but simply adhering to structure and order, things that can apply to a theives guild with very clear rules on how they conduct business.
Most real-world mobsters would be LE.
There's always the possibility of an allied collective of shady types that focus on different things like a smuggling ring, burglary etc. Easy to work together when necessary, but not obligated to agree 100% with everyone's motives. Often there's that bully in the guild that people thing take it too far, as an example
That can work yes, and may be the better idea, an NPC who acts as a Fixer for shady types, matching up people with jobs or needs. It worked well for a while when a DM did the samething for the evil types, it was likely the most fun I had with Evil Valar, you had several smaller Evil groups who had the same ally who may have had radically different plans but the NPC smoothed it over.
The same could work for a 'Thieves' Guild, a Fixer who matches folks up to jobs, so for example 'Erliza doesn't kill on her jobs, so this B+E is a really bad match for her, better not let her know about that job, but this other job, matches her talents.' Meanwhile the less... picky Rogue type gets called up for the B+E it just means a lot of work for a few DM's and such things can collapse without it.