They don't make people thinner -- where'd you hear that craziness? You can get MUCH thinner when going through chemotherapy for lung cancer. Smoking doesn't make anyone any thinner. When smokers quit, they tend to get heavier because they replace cigarettes with food, but smoking wasn't making or keeping them any thinner.
a lot of celebrity women smoke because it suppresses eating. I think that's why people assume that if you smoke you lose weight. but its quite the contrary. once you quit the habit you gain a lot of weight because you haven't been eating, it slows down your metabolism.