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Facebook and Twitter are no follow links, which means that there is no benefit at all to your link profile. I agree with Robert mostly. Since these links are no follow, the key terms will only help if users are searching the respective social media platforms for your product. The benefit to SEO from Social networks comes solely from the trust factor social signals send. High engagement tells the engines that you are a reputable business, and, as we continue through 2015 most SEOs expect these social signals to increase in importance. I would recommend that you use your social media to build popularity and increase your audience. Stuffing your pages with keywords will have absolutely no effect on your SEO rankings. The exception to this is Google Plus. Posts on Google Plus can influence the SERPs of people who are in your circles. For example, when I am logged into my MCC account and I search for one of my key terms, I often see my Google plus posts in the results. Other than that, there is no benefit to that platform either. Here is another post with some more information I might have missed. Hope that helps!