Back before school started I did a presentation at our district wide professional development on social media use for educators. I've been an avid Twitter user for years and it's been an excellent source of ideas, resources, and professional networking. To a lesser extent I've also used Facebook and Google+ and from what I've seen there is a huge community of educators on Instagram as well.
My fellow ITRT Sara Butcher and I had put together a presentation on Twitter for Educators last year after attending a presentation on it at the VSTE conference a few months prior. (And to be fair, borrowed a few things from that presentation as well.) I took that and expanded it to include the other three networks mentioned above. My plan is to expand it further to include other networks such as YouTube and Pinterest and use it again in the future.