Well, telling by the avatar, you do have a lot of weight to lose, and the reduction in body fat will definitely reduce the appearance of the double chin because there's less fat. It greatly depends on the amount of excess skin. Make sure that you're keeping or gaining muscle in the process.
Second, there really isn't any specific exercise that would target the chin because there really isn't any muscles there. The neck however, is targeted indirectly from a lot of exercises because the neck always gets some sort of tightening as a way to stabilize the body.