Okay, blushing is nice and cute but it also states that you are not confidence. And I am not saying that is a bad thing I am just stating it so you understand how a guy is interpreting it. My suggestion to you is to smile (really smirk) and nod back to him acknowledging that you noticed him looking at you and appreciate the compliment. Because it really is a compliment right, he is staring because he finds you attractive. It doesn't mean anything has to develop from it and technically you don't have to talk to him. He is just saying you are attractive. Now by you nodding back you are putting him on the spot and he has to make a decision. Do he approach you or not. Must guys will not approach because they are afraid to make that move. Many will not approach because that is all there is to it meaning they just find you attractive and don't want anything else.
Flirting is awesome...I love flirting but it gets me into trouble because it always leads down a road I don't always want to go. So understand just because you flirt back does not mean you obligate yourself to anything. Just when they approach if you want to talk to them talk, if not then let them know that you are not really looking for anything serious and appreciate the compliment and go on about your business.
Is there are reason why a "Teenager" under the age of 18 is looking for a "relationship"? Do you really think a guy is looking for a "relationship" at that age? Be smart and develop your "independence" first. Always ask yourself these two questions; what am I bringing to the table and what is he bringing to the table? If the only thing you can offer at the table is the hole between your legs then guess what you have a lot of work to do before you can be in a relationship. And if the only thing he can offer you is the stick between his legs then guess what he is not ready for you. For the rest of your like guys will be looking at you, whether you are pretty, ugly, fat, tall or small. Immature Guys don't care to be perfectly honest. Get your own stuff together and you will draw a better more mature and qualified group of men to you.
Im late to this but the best thing to do if you do like the guy that is giving you the attention is to smile at him.If he smile back then that's great and you're letting him know that you are available to talk to.If you really like him smile and then look him straight in the eye and keep looking unless he looks at you and then looks away.Let him break the gaze.I always like it when a girl smiles and then blushes a little,it looks cute and lets me know that she might like me when she does that.Also its a turn on for me when a girl I give the attention to seems a little nervous while I'm around her.