Dont write off teens and Facebook just yet. A report released by Forrester Research on Tuesday showed the worlds biggest social network is still by far the most popular among US teens despite the rise of new apps and services like Snapchat and Tumblr. The results were clear: Facebook remains young users favorite social network. More than three-quarters of online youth use Facebook — twice as many as use Pinterest or Tumblr or Snapchat, and more than use Instagram and WhatApp combined, said Forrester analyst Nate Elliott.