Well you should first check if this guy is shy around girls he likes. Remember that shyness and being uninterested are often mixed up. This is why shy guys or those who have difficulty with social communication often come off as uninterested when in reality they may actually really like a girl. Trust me, I have this problem and i'm trying to work on it because you can't get anywhere if you never at least show some interest. The best way to talk to a shy guy is to be the one who initiates the conversation because shy guys have difficulty starting conversations. If you're the one who starts the conversation, then you may find he's actually a pretty cool guy and may open up to you more.
These are just some examples if a guy likes you but he's shy.
1. He has trouble looking at you in the eyes. He acts more open and friendly to other people but closes up when he's around you because he's nervous when you're around. A good test is to catch him looking at you and if he immediately looks away then he probably likes you but he's shy.
2. When a guy likes you he will try to impress you. But for shy guys, he tries doing this indirectly. For instance if you two are in the same class, he may say something funny and look over to see how you reacted to his joke. He's trying to get you to like him indirectly because he's too scared of actually talking to you. I think the goal of this is to get a girl to like him so either he knows she likes him then he can make a move or she will initiate the conversation which is every shy guys dream.
3. When a guy likes a girl, he wants to be around her. He's always glad when the girl he likes shows up and is disappointed when the girl doesn't. For instance, class, youth group, work etc... But for shy guys this may be less obvious as they try to not make it obvious they like you because he's scared you may not like him back.