The bulk of the surveys done for the Pew study were completed last September, and the social media landscape has already shifted dramatically since then. Instagram has racked up more than 100 million total users. Snapchat, a photo messaging app popular with teens, has exploded in popularity, now sending 150 million messages per day. And Tumblr, which boasts a youthful demographic, was just purchased by Yahoo. So far Facebook has warded off (or bought out) all competitors, but its tight grip on the youngest demographic is weakening.