I really liked this website
http://www.scoop.it/. My ESL middle school students are fanatics with Facebook and Twitter. I would like them to know that you can post other things than conversations, what you did that day, who's hooking up with who and other mundane topics. This website has the student smartly research a topic, add their perspective and publish it on their various social medias. Of course, Facebook and Twitter being the biggest! I think my students will surprise themselves that a smartly researched, pertinant teen topic would generate allot of meaningful conversation!