There is no direct proof that social signals impact ranking.
In 2010, Matt Cutts, Google’s Head of Anti Spam, released two videos on this topic: one in May stating that they were not using social signals as a ranking factor and one in December 2010 saying that, at that time, that they were beginning to use social signals as ranking factors, though he cautioned people that Google would consider quality of followers as a ranking factor rather that number.
In a later video, in 2014, ha said that Google treats social posts like any other web pages for search but NOT as a ranking factor because Google is limited in how much of the social web it can crawl so it is missing lots of data and therefore cannot judge on the authority of those pages.
This is probably due to the fact that Social Media are volatile environments where information changes very quickly especially about relationships or following: one account may have large numbers of followers and one day do something which causes a lot of the followers to abandon it so Google can’t be confident enough in the authority of a social account to consider it a ranking factor.
So the position of Google about this topic has changed over time along with changes in search algorithms and in the way social media function.
The position stated in the 2014 video, seems to be pretty final: Google does not treat social signals as ranking factors. Nevertheless, top-ranking Urls tend to have more social signals than those that don’t rank as well. It is co-occurrence rather than causality, and the details will probably remain a mystery, but one thing is very clear: search engines like to display high-quality, relevant content, and that’s the exact recipe for high engagement and a strong presence on social networks. The positive effects from social media as it relates to search can’t be ignored: likes, tweets, and +1s raise brand awareness, improve traffic, and enhance the performance of a domain. It is enough to consider integrating social media with your SEO strategy.