Dan from Trulia here. There are multiple ways for you to advertise on Trulia. The link I've included is for our new Local Ads product, which is in limited release right now. This service allows you to set up your own ad and then pick a share of your local market to buy. You can choose any set of ZIP codes or cities.
You might also consider Trulia Pro, which allows you to set up a Spotlight Ad that you can use to target Trulia users as they search in your area. You can learn more about Trulia Pro here: www.trulia.com/truliapro