Well since I can't exactly say you should just beat him up, I will say you should at least do more than tell him off.
1. Maybe he really likes you but he's too afraid to tell you.
2. Maybe he jealous that you stole his girlfriend or something.
3. Maybe he just plain doesn't like you.
4. Maybe it's just the way he is and therefore does it to more people and not only you.
Whatever the reason is, there is probably a high chance this will persist. You could "tell on him." Tell someone who's over the age of 20 who will care enough to listen and do something about it. This is least likely to get you in trouble, most efficient to get him to stop but has the highest chance of you getting scolded by your peers leading to distrust and rumours. Yelling "STOP STARING AT MY ***" In a crowed area should embarrass him into stopping as well.
I bet you anything he doesn't beat MY creeper face tho.


Best of luck, Gabag.
