Yeah, I hear you. It's better to keep those kind of things to ourselves, even from close friends, until they have a chance to develop into something. The only time it makes sense to tell a friend is if you actually need their help with getting closer to the person, otherwise they tend to try to take things into their own hands.
Just stay cool, and if the guy is worth the trouble, he'll come around. If not, it wasn't meant to be.
Good luck!
BTW, I once told some girl that a friend liked her. Well, sort of... It was worse... I sent a message pretending to be him. Anyway, he kept talking about this girl and wouldn't do anything. Turns out he was totally in love with her and wasn't kidding. Woops. He didn't speak to me for like a year. That's how I learned to keep my mouth shut and not ruffle lovebirds' wings.