After Facebook bought Instagram in April 2012, its traffic skyrocketed It is now the largest photosharing site in terms of unique visitors.Micro-sites Twitpic, MobyPicture and yFrog saw unique visitors decline in 2012.Combined, Twitter, Tumblr and Posterous still do not match Facebook’s unique visitor numbers.The big three: Google, Facebook and Twitter. The statistics do not differentiate between Google search and GooglePlus.