Guy in my school keeps sexually harassing me...?

Theres this popular guy in my school whos ONLY perverted with me. Everyone else thinks he's so funny and chill, but I've seen his true colours. In the beginning it wasn't that bad, I mean he just used to call my name and tell me to come to him (even though I had no idea who he was), and I used to ignore him (cuz I found him creepy). Then it started getting gradually worse. In the hallways, he'd quickly put an arm around me while he was passing by, then he started checking me out really pervertedly, and at first I think it was cuz he wanted to make his friends laugh, but then he started doing it even when his friends weren't there. Then this one time when I was at my locker, I felt someone touch my butt, and when I turned around it was him. Now he's been touching me a lot- some days he touches my butt, and other days he touches my breasts (he does it discreetly). It's making me feel really disgusted and vulnerable. Like to EVERYONE else he's so sweet, but I don't know why he's so perverted with me! Why does he have to bother me?? I barely know who he is. I'm way too scared to snitch on him because I know everyone will hate me if I do, and it's not that long til school ends, but I'm really scared that since school is ending, he'll do something way way worse to me soon. I'm also really sick of the feeling I get before I go to school each day, always anticipating what he'll do next. I'm not the kind of person who gives reactions to those kinds of things, I try my best to ignore it, but he's getting creepier and creepier. What should I do??