how do I tell my crush I like him?

Well sadly at the moment, we are becoming less more romantic and asking via SOCIAL media, big sigh, but there are reasons who wants to be rejected in real life or anywhere... Plus it really depends if you want something out of it. Do you want to date him? become friends? friends with benefits? It depends. 

I suggest you hint it to him or just directly tell him you like him, it doesn't really mean you're asking him out so he can't exactly deny you, you're just telling him, or you could just give out the vibe you like him and like if he sort of knows and is responding more flirty or nice or whatever... he probably likes you too and is picking up the hint , or he may react differently, ignore you, not talk to you. But I don't think this will happen. Just be yourself and tell him.