Klavika  Suggested by donshottype 

Custom, derived from Klavika

https://www.underconsideration.com/brandnew/archives/new_logo_for_facebook_done_in-house_with_eric_olson.php#.VZrSb_lQCSc

donshottype, what you are saying is that you need an exact source, I do not think it looks like Klavika or probably it is not a source

My reading of the article linked in my post is that, although the new facebook logo has significant differences from Klavika, it is indeed derived from Klavika.