I know that there are a lot of people with bipolar disorder that go to free DBSA and NAMI meetings, at least on occasion. Perhaps those folks prefer the in-person support over online. I also know that there are some very busy Facebook groups. I would never join those, personally, because I want to remain as anonymous as possible. Though I do visit online support groups, I also blog and follow blogs that address mental health issues.

I used to be a group leader for an online bipolar support group on another website. Many people come and go. I think that either they get too busy with daily life (work, children, both), start to dislike support groups, find therapy is enough, get sick and tired of thinking about mental illness, have uncomfortable fights on the group (or are bullied, as sad as that sounds), or are too sick with the illness to be posting online. Some people with bipolar go into denial, or avoid groups because they refuse medications and don't want to defend medication non-compliance.