Social media marketing and search engine optimization are both ways to promote articles in content marketing. They are both inbound channels. But they are very different from each other. In fact, social and search are opposites in many ways.
SEO is about being discovered and getting traffic through search engine rankings. It fills the top of the funnel and creates awareness. Whereas Social media marketing is about connecting, building relationships and getting traffic from social media networks like Facebook, Twitter, Instagram, Pinterest etc. It strengthens the middle of the funnel and creates engagement.