Social media was not originally a part of SEO, but that is changing. Google is now sending out its bots to crawl for “tweets” and “posts” and also developing other ways to determine whether a site is strong in social media and then using this information as a factor in determining the overall quality of the site.
Just as links are a sign of popularity among websites, social bookmarks are sometimes signs of whether people approve the content or not.
The important factors in considering using social media for SEO is relevance and quality. I feel that the importance of social media is growing and in order to maintain search quality, search engines will need to pay attention to the social side of the Web so having a large social reach will likely reflect positively on SEO results.
If you need help in this area, get in touch with me!