This is an idea - simply put Google as far as is known anyway doesn't have access to Twitter or Facebooks info on the backend so they may not know the difference from a post with 10 natural likes or retweets vs one that was bought from Fiver. Social may help in other ways such as conversions but it seems like socials effect on serps may be minimal at best. This is not to say anything against social. Some websites may even have big traffic boosts with it but simply thay it isn't the same as links or on site content. If anyone has ideas about this feel free to chime in.