On the more well known and used networks they quizzed over 300 regular using scholars for each analysis whereas with ResearchGate this moved up to just short of 1,600.
From our, very uneducated & superficial review it is clear that a majority of scholars/researchers don’t use Facebook professionally and that Linkedin has the closest profile to ResearchGate. Twitter almost as one might expect is used to follow comment and discover.
ResearchGate which was founded a couple of years ago boasts about 4.5 million subscribers and currently joiners are arriving at the rate of 10k a day. This for such a specialist network is impressive. For comparative purposes Academia.edu has around 11 million users and Mendeley around 3 million. Mendeley incidentally are London based and are part of Elsevier.
Much additional and insightful analysis on the Nature site.