FaceBook and Twitter Are Not Socilial Signals Used for Ranking
I have been saying this ever since Google abandoned their attempts to use social signals for ranking purposes in 2012. Here is the word from Matt Cutts.
It is also getting really tiring to see all the scammers on sites like Warrior Forum who continually sell plans that will rocket your site to the top of Google through social signals. It is complete BS.
The blocking from a social network that he refers to is when they had a falling out with Twitter and Twitter banned GoogleBot from the Twitter site.
Almost all links from social network sites have the nofollow attribute, so backlinks from social networks do not help.
Use social networks if you like them or believe they will drive traffic, but do not count on them for improving Google rankings.