I cannot detect any problems with the following code, but due keep in mind that it may take up to 48 hours for the effects to completely change. I had this problem at first, i swore my code was correct but low and behold, about a day later the links where working like a charm. Keep trying to check the thumbnail for another day or so and if the problem has not yet been fixed, i shall attempt to remedy another solution.
Edit: As of 10/14/2012 @ 3:13a.m. central time, ‘MERICA, your link on facebook is displaying a default thumbnail of a lady with a total of 4 pictures (the lady, a black dude, twitter icon, and facebook icon).