It depends on what he likes. I'm a workout freak and my girlfriend is a bit overweight but I love her to death.
I won't lie, at times I would glance at another lady for a moment but I then look at my woman and say to myself "man I'm the luckiest guy to be this girl"
Most of my friends that are skinny tend to date another skinny chick. My girlfriend brother is overweight and he married and good looking skinny chick. Like I said, it depends on the person. but most men prefer woman with meat on their bones.
I'm a toothpick, and I love chubby girls. I'd rather go out with chubby girls, than with the skinny models you see on FashionTV. I know you didn't mean fat, but your question is based on skinny guys. Being curvy has nothing to do with weight. The opposite of curvy, is flat. You can be curvy, AND skinny. It's all in the arms (which I notice, BTW, not sure if other guys do), and legs. If a girl has have big boobs, butt and hips, but arms look skinny, I think that's a little bit weird.
So to answer your question, as a skinny guy... yes, I do like curvy girls. But no, I don't tend to go for skinny girls.