Does effective "Social Media Marketing" mainly focus on PAID advertisements on social media or FREE organic promotion?

By definition, Social Media Marketing (SMM) is related to 'paid' ads. It is similar to Search Engine Marketing (SEM). Both deal with the paid ads.

Search Engine Optimization (SEO) deals with the free, organic results of a search engine. In this is included your company's presence of social networking sites like Facebook, Twitter, etc.

Between the two, paid and organic, studies show that organic is more effective. However, it is very difficult and time consuming process to improve organic results. Paid results can easily be acquired if you have that kind of money.