I don’t know what the situation is with your keywords, but for many of the keywords I monitor, Facebook has consistently been ranking near the top for the last 3-4 months. Even if it isn’t in the very top spot, it is appearing in second or fourth place. Here is an example:
https://www.google.com.tr/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=metin2%20pvp
They fluctuate between the 4th and 6th positions, and two pages appear in the search results. Additionally, I almost never see Twitter in the search results. When I check my secondary keywords, Twitter pages are always at the bottom, while Facebook is always at the top.
I remember Facebook wasn’t this strong in the past; did it gain this strong position through an update? What is the situation with your keywords?