Pew notes that for now it looks like Facebook is partly winning because of how it has managed to appeal to a wide range of users — a pretty impressive turn for widening its reach, considering that it started out as a network restricted only to university networks.
The demographic data for other networks stands in contrast to this: Pinterest “holds particular appeal to female users”, with women four times more likely as men to be Pinterest users; LinkedIn is “especially” popular among college graduates and internet users in higher income households. Twitter and Instagram resonate with urbanites and younger adults, and non-whites. (Facebook has over 70% usage among whites, Hispanics and black users, Pew notes.) All of them, excepting LinkedIn, has its highest proportion of users in the 18-29 age bracket; LinkedIn is more popular with the 30-49 group.
Among those who say they use only one social networking site, Facebook is a clear winner with 84% selecting it as their sole site, with the others lagging behind by a very far stretch: 8% solely use LinkedIn, 4% solely use Pinterest, and Instagram and Twitter each picked up only 2%