<Why social media will never be a ranking factor:

Already most brands makes a lot of mistakes when it comes to social media as seen in this post but thinking that social media will affect their Google ranking should not be one of it. In all over 200 Google factors are used in ranking and almost 90 percent of these have never been openly confirmed by Google. According to Google, all you need do is add your keyword to your page’s title and drop the keyword somewhere in the body of the webpage. Then go ahead and create “great” content that people "want to link to" and you will find people linking to your website. This will then make your ranking to increase. In reality, it doesn't work that way. No one can fully understand how Google determines how pages are ranked. To understand this, just enter some of your keywords in Google Search page and then measure factors like contents, backlink profile on the results and you will be surprised as to how some website get higher visibility even in post panda and penguin updates. But we should not blame Google. Afterall, it is just a machine. Here are my top reasons why I believe social will not be a major factor in website ranking.

You'll want to read them all but I like this one particularly:

3: Google must be seen as the impartial judge

Google has tried as much as possible to maintain its integrity even though we all know that business exists for the major purpose of making profit.  Now suppose Google suddenly start taking into account social media to determine your website ranking. Who will get the upper hand? Will it be facebook with over 1.5billion people or Instagram? What will be Google’s algorithm for determining this? Any website with 10,000 followers on twitter will get higher ranking for “Keyword” on Google SERP irrespective of how many backlinks they have? Or will Google say something like this: If your post gets re-tweeted 20times by 20 people out of the 5,000 followers you have or by 20 people out of the 20 followers you have, than you deserve a higher ranking irrespective of whatever you have posted? Suppose our analogy work that way, in these days of promoted tweets, buying followers and likes, how do we know people who won their followers? Will social media share their algorithm with Google to enable Google understand how they work when Google has continuously kepts its inner working secret? I don’t see that happening any time soon>

Google ranking can't be gamed.  Yes.