The May 9th NYTimes has an Op-Ed essay, It’s Time to Break Up Facebook, by Chris Hughes, the co-founder of Facebook, calling on the government to break up that company. The essay is very thorough in describing the current monopoly behavior of Facebook, the deleterious effects on competition and vigor in the economy of monopolies, and a great introduction to the history of anti-trust movements and legislation in the US.
One should note that you can apply exactly the same descriptions and call for anti-trust action to almost every sector of the US economy. Read our essay The Monopolization of America for more on this wide spread phenomenon. And for more about internet monopolies, including Facebook, read The New Digital Monopoly Capitalism .