A recent New York Times article, Should Reddit Be Blamed for the Spreading of a Smear?, raises the question of whether social media sites acting as "news" outlets should be held accountable (morally and perhaps legally) for misinformation. Immediately following the Boston Marathon bombing, users of social news site Reddit incorrectly identified one of the bombing suspects. This incorrect identification resulted in media attention to and harassment of the family of the misidentified suspect, who ultimately committed suicide.
The First Amendment to the Constitution identifies what we commonly think of as the freedom of the press. What does that right mean with the advent of new media? For a starting point for your inquiry, check out Free Speech in the New Media.