There are currently three big social networks built specifically for scholars and scientists: Academia, Humanities Commons, and ResearchGate. This page offers a quick summary of each, presented in alphabetical order.
Is one of these options better than the other? Should you use all of them? That's up to you. But perhaps the most important question to ask is where are your peers?
A for-profit social network for academics. Founded in 2008, Academia now claims over 150 million users and has focuses its efforts on getting more readers for scientific and scholarly papers by building a private library of PDFs provided by its users. Like ReseachGate, Academia contains many files that are being likely being shared illegally.
Launched by the MLA, Humanities Commons is an open access, open source, and nonprofit social network for scholars in the Humanities and Social Sciences. The Humanities Commons network is open to anyone, regardless of field, language, institutional affiliation, or form of employment. Full-featured accounts are and will remain free for individual users; the network is sustained by the financial contributions of participating organizations.
A for-profit social network built to connect STEM researchers and scientists. ResearchGate was launched the same year as Academia and while it has grown significantly Academia is much larger as measured by the number of papers (22 million vs 100 million) and number of registered users (150 million vs 15 million).* Like Academia, RG has built a library of scientific papers, many of which may be shared illegally.
*The data for Research Gate is based on 2017 numbers as no new numbers have been published on their website.