Great question! Along with the ability to have your Facebook Ad appear within a certain geographical area, you can also narrow your audience down by choosing from hundreds of different characteristics, such as pages liked, comments, check-ins, and user behavior. Here is our FAQ page that briefly discusses How Facebook Advertising Finds Your Audience.
For Information on this and getting started, feel free to call or email our Facebook Advertising team.
They can be reached at 1-855-816-6502 (Mon - Thurs, 7am-11pm ET and Fri 7am-9pm ET) or email at Facebookads(at)constantcontact(dot)com.
I hope this helped get you an answer. If you are looking for something else, can you tell us what ads you are running, please? Are you using a Constant Contact feature or product?