Social media outlets come in every form and fashion you could possibly think of. Depending on demographic or geographic location, there are many possible places you can put both yourself and/or your brand.
Facebook seems to clearly dominate the market (as we all probably know), but Ignite lists a breakdown of analytics from most of the worldwide social networking sites. These insights include: age, income, gender, education, search traffic and along with many more.
This only proves the point- do your research!