In December 2015, Facebook had 21,390,733,000 US visits on both Desktop and Mobile, vastly more traffic than its 4 biggest social media competitors, Twitter, Instagram, Reddit, and Pinterest. In comparison to these competitors, Facebook takes home 78% of the traffic share, leaving 22% to the other 4 social networks.
Instagram dominates the East Coast, West Coast, and is the second most popular social site in 4 out 5 of the most populous US states including California, Florida, New York, and Illinois. Texas, the one state missing from that list, is apparently Reddit territory. Reddit, in fact, is the preferred social network of most of middle and rural America, but also boasts Michigan and Massachusetts in the east. Twitter only captures 12/50 states.