you can do a 1000 sit ups a day, you'll get rock hard abs but if theres a layer of fat then it wont look it.
you can target a certain area unfortunatly, an overall body fat burner will work, cardio and some weights will both make you lose the fat and tone up.
heard of the term skinny fat? people who only do cardio, are usually in this one. add some weights (dont worry, it wont bulk you up) and it will tone aswell as lowering body fat percentage
hope this helps