Heres a list of 3D Printing Communities on Google+ and the amount of users each one has. If we missed a group or need to add one please comment below. Also we added the most seen Admin/Mod in each Group. As time goes we will make a new list every quarter so you can see how each group expands. Below Ill link the Facebook list and a PDF for the Total G+ List.
Biggest 3D-Printing groups on Facebook – <– THIS IS THE FACEBOOK LIST
3D-Printing Communities on Google+ GOOGLE+ PDF LIST
(100 users and up, Groups missing could be because of hidden user amount)