Ross Dunn and John Carcutt go through 8 Ways Social Media Can Impact Your SEO. They go through the list below:

Brand Awareness: “people who have heard about you on social media search in Google for branded keywords” – no = search behaviorLink Potential: “social sharing can result in citations and links”Personalized Results: “Google+ posts rank in Google; +1-ed content ranks higher; pictures of authors in your circle are visible”Increased Domain Rankings: “the more your content is shared, the higher your rankings will be.”Social Media Sites Get High Rankings: “your social media pages are likely to rank in the top 10 for your branded keywords”Google+ Impacts Local Search: “reviews, +1s, verified pages, local area codes, complete profiles and more all help you to rank higher.”Relevant Keywords: “your social media posts will rank for keywords you includes”Faster Indexing: “social media shares can significantly speed up the content indexing process”