There`s a correlation between activity in your official page in FB and number of people who requests about you in Google. So promotion in social networks can indirectly effect your SERP position. Just recall it it when you think about Panda, Penguin or Tiger. Traffic attracted from FB or G+ imho is goddamn new SEO. Old SEO is dead. New one is based in unique viral content multiplied with social networks. Are you agree?