From a SEO perspective FB likes does nothing at all... In addition getting fake FB likes is easy just head over to fiverr and you'll see.... so its easy to understand why G does not use this for its ranking algo... In actual fact G has stated publicly that this is the case... Here is a good article which discusses this
here.
In addition FB has fundamentally changed the way likes work with sharing content on FB. The organic reach is now around 10% where as before it was all of your fans which liked your page would get an update on their newsfeed... That is because FB is encouraging you to use FB ads...
That said getting real FB likes will of course help with traffic as people are engaging in content ... and some may even share pages and provide backlinks - hence why some may attribute FB likes to ranking on the serps - but the reality is that this is cause and effect... An indirect one - which many interpret as rationale that it helps with rankings... but again its not the case...
That aside having a good number of FB likes does add credibility to actual real visitors.... However too much also screams out that its fake (well to me it does...)...
In addition I would also try to get FB shares e.g. ask visitors to share content on FB, twitter etc in return to access additional info, download report - as that can bring in more traffic to your site.... So shares and likes do help but it will not directly influence your SERP rankings (only indirectly for the reasons mentioned)....
