Starving yourself won't make you lose the fat, or make you lose weight. The body has defensive mechanisms against starvation. First it limits its calorie consumption to a bare minimum (may feel weak, dizzy, sleepy), then once it can't hold back any longer, it starts to suck your fat and muscles dry. Humans need fat to survive, so it's definitely not a good thing. And you need muscles for just about any movement you can think of, so that's not a good thing, either. I'll let you do the math.
Rather raise your calorie intake a bit and start working out.
Doing ab crunches is definitely not going to give you a six pack, so feel free to do them. I'd also suggest a cardio workout, cycling, running, stair walking, jogging, even walking longer distances is fine. Do it three times a week, at least for 30 minutes. It'll get rid of the extra fat, and make your body look toned and smexy (cycling makes your legs and behind look yummie).
It's one thing being toned, another thing being ripped.