They might be hungry due to normal hunger but if you mean in reference to maybe them starving themselves to stay thin? I don't think so.
I'm amazed at the amount of maintenance calories that some of the ladies here have to consume to hold their low weights (I say ladies just because they traditionally have low weights compared to the men). There are some ladies here who weigh 140lbs (that is a low weight to me!) who eat 2000 calories or more a day. If you are eating healthy, that's a lot of food to get in. And I don't think any of them walk around hungry, at least based on what they post here.
The thin people that I know who eat junk all day, they seem to be more hungry but I think it's the sugar and fat overload they give themselves. Some of them are blessed with better metabolisms and some of them kill themselves at the gym every night so they can eat crap food.