Social signals according to Searchmetrics are not a ranking factor.
However, their "Search Ranking Factors & Rank Correlations 2015"... which provides webmasters, SEOs and content marketers with the latest insights regarding the most important ranking factors for high-ranking Google.com search results.
They have stated the following...
"The question remains open as to exactly how social media signals such as likes, tweets and +1s boost rankings. Google...