There is quite a bit of overlap between social media and search engines. More and more often you're starting to see people turning to these interactive platforms for all sorts of functional reasons that go well beyond the 'social' aspect of things. Twitter has very much established itself as a one-stop shop for news and fun, Facebook is a sphere that has become almost essential for business promotion alongside the multitude of other purposes it serves, etc. These corporations have come along way in terms of expanding the search capabilities they offer and boosting their overall level of versatility.
Although we're long past the point of no return where social media started playing an integral role in society, it certainly hasn't replaced the function of more traditional search engines. Moreover, it is still being integrated into their ranking processes. The powers and mentalities of these search engines are constantly evolving, and the rise of social media has played—and will continue to play—an enormous role in that transformation. As things stand right now, at the beginning of 2017, here are some of the most important ways in which social media supports SEO.
1) Traffic
Search engine optimization isn't something that can just happen overnight. It requires a demonstration of many things in order to actually produce that coveted first-page ranking. Where social media can begin to help with that is by bumping up traffic. It is actually remarkable when you stop to think about it just how powerful a distribution tool social media can be. If a prominent celebrity dies, even the most casual of social media users is likely to find out within the hour. Sometimes it is even social media that drives certain outlets' coverage of a story ("Twitter reactions to such and such event").
Domains that have pages shared on social media reap their reward in traffic numbers. Even though it is social media sites and apps that facilitate the visits to these external webpages, the traffic metrics are filtered back into the more traditional search engines after that visit takes place. Social media is unprecedentedly effective at enabling traffic levels that would otherwise likely never be so high.
2) Engagement
Along similar lines to what traffic accomplishes, social media advances engagement, which in turn boosts SEO. Remember, it's not just about whether or not you check something out, it's also about how you do it. For example, search engines keep track of a statistic called bounce rate. If you click on a link to a web page but then "bounce" immediately and leave, then it'll count towards a higher bounce rate for that page and lower its ranking.
Engagement could also occur as a result of a successful call to action on the external site, which would have only been made possible because of social media. So in this regard, social media is the vehicle that gets targets in the door. It may not produce the same type of promising lead that an AdWords campaign would, but having quality and quantity is rarely a bad thing.
3) Search Results
You may have noticed that social media often shows up on SERPs (search engine results pages) when it is relevant. While this is no doubt a net positive for a website in its quest to rank higher, having a Facebook or Pinterest post show up isn't the same as actually ranking with your own domain.
As Google spokesman Matt Cutts has explained, his search engine treats social media posts as they would any other page for searches, but not for overall rankings. In other words, a successful social media post will not have the same effect on Google's ranking algorithm that regular successful pages would just by virtue of social media popularity.
4) Indexing
Indexing is the process by which search engine bots crawl through pages of information on the Internet so that it can be better understood and brought up properly in search engine results. Social media has given search engines an enormous spike in pages that must be crawled, since the volume of posts that get published every day is enormous. But for those who share their content or have it shared via social media, the increased exposure means that the content may be discovered and indexed faster than it otherwise would have been.
5) Google+
Call it tech nepotism if you will, but using Google+ as a social media vehicle provides users with an opportunity to gain a distinct SEO advantage. The reason for this is that Google+ searches are very much curated based on the activity of a network's feedback. For example, if you are in a circle with someone on Google+ and that user has +1'd a page, then that page will rank highly for you when you search for anything relevant to it. A regular Google search is more objective towards the general public, but Google+ offers the opportunity to build traffic—and eventually SEO merit—by capitalizing on this effect.
6) The Future
Social media is already a massive phenomenon in the present, but it still has a long way to go in terms of how it will be factored into SEO. Even if the SEO benefits may not seem hugely enticing to someone today—though they still should—search engines constantly update their algorithm and social media should only become easier to track and more vital to rankings going forward.