I think that I have written about this in another post. However Google + has great communities that people can get involved in. I have joined communities and asked permission if I can post my link if it is relative to the community. They community owner had no problem with it, and even if it does not directly effect my serps, it is engaging potential customers which is valuable.
I think it does effect Serps though, I posted up a graph I put on pintrest.
FYI, for the link to be do-follow it must be posted and inserted within the Google plus, not just shared from your website.
Another thing to take into consideration is that many social media guys claim that using bitly on facebook and twitter help the crawlers find your link and because it is a 301 redirect not a 302 it is a do-follow. I am not sure about this, I think the article was from Don Crowther
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