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...

Remember that time in high school when you realized that the best way to get instant popularity is to hang out with people who are already popular? When being a part of a clique or gang takes your “image” to a whole new level?

That applies in online marketing, too.

Being associated with influencers not only...