Chase Ambulances :)
Seriously though, I have a friend who is a chiropractor and he has an annual customer appreciation BBQ. He invites all his current and former patients and their families. He gets a lot of referrals (and renewed visits) that way via word of mouth. Also, the crowd having fun in the parking lot is sure to attract attention from passers by.
He engages directly with his patients on social media too -- and not with some automated tool or disinterested intern or social media expert. How are you doing Bob. Thanks for coming to the BBQ. A personal anecdote, etc.
A personal blog that talks about the practice, engages employees, has informative articles about wellness and links to relevant news is also a nice touch, and gives you something to share via Facebook, Twitter, etc.
I've helped several people with social media, Google AdWords, Facebook & Linked In ads, etc. It really helps to have a coordinated effort between content, personal engagement, social media, and ad campaigns together.
One other aspect that is like that virtual BBQ -- is a regular newsletter that patients and other interested parties can subscribe too. Build an email list and give people something to read & stay in touch every month -- and print a few copies to set out on the front desk.
If people click on an ad, it doesn't have to translate directly into an appointment, maybe a slow nurture campaign with a few tips for dealing with back pain and general health (getting a good night's sleep, etc.) is a good way to get people to slowly engage until they've gotten comfortable with you and then come into the practice or give you a call.