Basically someone asked if anyone has a google+ account and a few people responded and I linked to the google+ thread, which was basically a "oh look at this shiny new thing" discussion. Perhaps just make an old fashion google group (lots and lots of people have gmail, dosen't need to be your real name like g+ or fb)?

I'm sure there is plenty of specialized stuff for this as well though, I'm afriad I'm not familiar with it though. I think there was some discussion on "what to use for a study group" here.