Google does not use social signals as a direct ranking factor. There are over 500 ranking factors in Google's algorithm; very few of them have been confirmed. Social signals seem - I emphasize seem - to be an indirect ranking influence.
Social media may be - I emphasize may be - good for establishing your branding and thought leadership, but getting engagement is pretty **** hard, unless you're a celebrity, a global brand or otherwise have a high public profile.
In order for Google to consider whether or not your social media engagement should be counted for indexing and ranking depends upon your followers engagement with the content you post on your streams.
I have mixed feelings about social media - on one hand, it can be very useful in transmitting near real time information during situations, but on the other hand, it's a total **** show what with trolls and the hateful fighting that social media seems to encourage.
Unfortunately, as business owners and web publishers, we are expected to participate in the appropriate social media platforms our target audiences frequent. Social media can be one helluva time and energy sucking exercise, because you really just don't know what will trigger good engagement consistently.