Pinterest: This is a great network if you have a blog with general health tips and articles.
Google+: You should create a Google+ page simply to enter in your business information, like your address and phone number, so it displays prominently when someone searches for your practice on Google.
YouTube: Video is an effective way to get your message out to prospects and participants. Good content for YouTube includes answers to common participant questions, tips on avoiding the flu and other viruses, as well as fun videos featuring your office staff.
Tumblr: The network of choice for hipsters, Tumblr might be a little edgy for a medical practice. Still if you have simple, visually interesting content, it could be a good channel for your business.