There have been a few jobs advertised of late for social media positions including at diverse companies like the Kenya Airports Authority, Nation Media Group and now Squad Digital (for Rwanda).
But there's more to these jobs than just being on Facebook or Twitter, and ultimately they are about communications - being aware & monitoring of what's being said or written, then communicating a company position to the public, communicating product features, changes & news, or communicating with customers in customer service - and to communicate properly, entails an understanding of media, marketing, campaigns, product cycles, consumer behaviour etc. This Citizen news piece gives a behind the scenes look at the currently widely-acknowledged corporate leader in social media engagement - Safaricom.
Not all companies are ready for social media, nor should they all be online - and while the current mediums are blogs, YouTube, Twitter, and Facebook, they may next be on others such as G+, Whive or Mxit, having come from engaging on company websites and email. But ultimately, it's about communications, not social media, and as @kaboro said - if all you know is Facebook & twitter, you’ll be out of a job before long.