CREEPY GUY FOLLOWING ME AT SCHOOL...HELP?

wow so theres this very creepy 10th grader at my school who likes me...no make that obsessed with me! ever since the first day of school he has always had this crush on me. i dont even know who he is because im in 9th and he's in 10th. but he'd see me in the halls and walk by me and give me this creepy annoying smile. the worse part is that he's in cross country with me and always stalkishly watches me there. at one of our races, he kept walking past me then would randomly walk right in front of me and stare at me *ewww*. then the other day when I was in the library doing homework i saw someone looking at my from around a bookshelf so i moved. then he followed me there and kept looking at me again. his cl is across from mine. so he will purposely stand right in front of my cl and "accidentally" bump into me! this is so ridiculous because he's a complete stranger and very weird and a stalker. what should I do?????