Technically all the study groups are 'still active' although some haven't been posted to for a while.
I think that folks come along and post here fairly regularly.
At the top of this forum you'll find an index thread with a list of all the threads in this group.
You can post to any of the older threads or if you want to discuss something that hasn't been studied just begin a new thread.
The best way to get a study group going again is to start posting in it and folks tend to come along and join in.