I agree with the research findings, but my reasoning for depression is a bit different. The primary reason is that Social networking sites have a certain amount of visual medium associated with it, by way of allowing the members to post photographs, etc... Now when you see your close friend from school posing for pictures at exotic locales abroad and you're in a point and time in life where going abroad is just a dream, unconciously it creates depression with you. This is just an example, but there could be more reasons for depression along the same lines.
