Guy sends mixed signals! Does he like me or not?

We are in the same university. He shows me all the positive signals, like staring at me from a distance, trying to know my relationship status, finding opportunities to touch me on the arm. Most importantly, he teases me a lot. And he also once said playfully, he knows I like him. But then, he ignores me on facebook. When we are in a group, he only opens his mouth to tease me. When we are alone, he is way too shy and we have nothing to talk about. He never had a relationship before. So i try to initiate outings (in a group) with him, and he does not even have the decency to say yes or no? Whats up?