Just came across this article yesterday. It is from May 2012, but it's still relevant. The sad thing, nothing has changed.
Bombshell! America's favorite social network is a child-predator playground
HUGE TRIGGER WARNING - the pictures are blurred for the most part but disturbing. This is part one of a series.
I looked up a few incest pages to see if they're still there - and then I just had to stop.
Incest family 47,000+ likes
Interest: Incest 132,000+ likes
Incest with Sister 19,000+ likes