What social networks are teens flocking to these days? That’s the billion dollar question as we see companies like Yahoo snapping up Tumblr in an effort to keep a younger audience. But teens are a tough audience to predict, and trends can change dramatically even in a single year. About 24 percent of teens who go online were using Twitter at the end of 2012, marking a dramatic increase from the 16 percent who were on Twitter in 2011. The new findings on teen social media use and attitudes toward online privacy come from a new report from the Pew Research Center, “Teens, Social Media and Privacy,” that’s set to release on Tuesday. Apart from the raw numbers, Pew conducted focus groups with teens across the country to get feedback on how they use different sites. Here are the five most important trends you should know about teens and social media.