I agree Jane, the role of social media in HR has grown exponentially over the past five years but still needs to improve.   There are examples here with DeVere where they have adapted to a social strategy. 

 There are many advantages for HR to use social media.  Clearly it makes the recruiting process easier and more successful by positing job openings on the company website and include links, increasing traffic to their website.  

Another benefit to companies in using social media is that they can browse the social media channels for potential candidates to determine their cultural fit (I'm not sure I agree with this having seen content on some of our candidate's FB page so best keep an open mind)! 

Social media also helps with company branding, allows you to monitor employee activity, and enables fast communication with employees - for example, you can promote company events so the public can learn about them. Other companies use messaging apps such as Google Hangouts to talk with employees in one location or all over the world.

Would be good to hear your thoughts about social media in the world of HR world today.