If no one is staring at you, then I'd take that as a sign that you're not doing anything out of the ordinary or offensive. I doubt that a whole group of teenagers would avoid staring just to be nice -- teenagers are not that nice. If everyone is staring, then it's a sign that you are not fitting in somehow. Some of the possibilities are ones worth worrying about, like having toilet paper sticking to your pants. Others, not so much (like you're wearing a fedora hat when fedora hats aren't cool).
It's okay to walk past people without looking at them, but realize that they are reading your body language and they might think you don't like them or are stuck up. If that bothers you, see if you can find a way to communicate friendliness in a way that you're comfortable with. For example, I can't handle eye contact but in high school I discovered that it doesn't matter if I make sure I've got a smile on my face. Posture also makes a difference. Walking hunched over staring at the floor makes other people edgy. Standing up straight and relaxed & looking around more at eye level puts others at ease.