Running, weight-lifting, and playing sports, etc. Those are all things you can do in order to maintain your shape, get stronger, and impress the ladies. However, in order for one to really answer this question, you have to be more specific as to WHAT exactly you want to "buff up." There are different things you can do for different parts of your body.
Well, there's many ways that you can get bigger, you can start taking suppliments, like protein shakes and stuff like that, but I think the best way is working out at least 4 times a week, working on your upper and lower body, if you have the will and determanation to do so for a long period of time, then I'm sure your going to have more muscles. But don't take pills like creatine or steroids, or even HGH to become bigger, because in the long run it's not good for you.
The best thing you can do is probably weightlift. Don't lift a big amount a couple times, but a smaller amount(not too small) and lift it maybe 20-30 times. There are machines at the gym that focus on specific parts of your body.
If nothing you do helps, then it could just be that your body just doesn't produce huge muscles, but it doesn't mean that you're weak.
I'm not looking to taking pills or any thing like that Vince. I want to work on all of my boddy but I don't want to look like I am some body builder. I have the muscles already, I just want them bigger.
Is there some kind of work out plan that I can do?
personally, note that i'm 14, go to the gym around 2 times a week. I do free weight work, machine work, crunches, push-ups, you can't just do one thing. I've been working out since i was 12 and i have really improved my muscles. and i'm one of the strongest people in my entire class (of 8th grade).