Yes, do them. I was 100% scrawniness till about Grade 11 in high school. Then I started doing a few pushups here and there... I hadn't seen my friend in a while, and when we got together, he noticed without trying to look for it that I had gotten a larger chest. I didn't notice, myself, obviously... But doing 10-30 pushups now and then (at once) helped quite a lot. It also helped tone upper abs.
You can gain quite a bit from doing pushups... so if you don't have access to a gym, go for it, it helps. Personally I'm too lazy to make a good habit of doing enough pushups to gain more, but I used to do em and I'm stuck at the level I'm at for now. At least I don't have to do anything to maintain a six-pack.
-RSI