Social Media won’t directly contribute to your site’s search engine rankings. If you find your Facebook page has thousands of followers, this has no impact on your actual website’s ‘popularity’. However, there are some correlations between doing well on social media, and getting more traffic to your site, and getting other sites to link to you. This is because ultimately your aim on social media is the same as what your website aims to achieve: you want to offer timely, relevant information to your visitors, and you’d like that to lead them to complete certain actions on your website (complete a purchase, sign up for a service, read your blog, etc).
So, it’s actually great content that is helping you on social media, and getting people to visit your site, and therefore improving your search results. The number of “social shares” you get is still very important because it indicates how interesting and relevant your audience finds your content. In this way, doing well in social media can lead to a process that ends with links to your website being placed. Additionally, the traffic that social media refers to your site is high quality, meaning that they are visitors that are genuinely interested in the content of your site.