Try: " Hi, (insert name here) I like you.
Add his name here: >>> _________, I like you.
Sending suggestive chat messages is usually a good way to start. Adding emoticons like ";)", ":3" and "<3" to your messages and being a little bit more intimate and closer to him. You know, the usual stuff. It's not very subtle, but also doesn't scream "I really like you!" in his face. Just playfulness. <br />
Gothguy's advice is also really good. Playing it off as a joke, but still being a suggestive. You'll need to decide what you can do, but subtlety is very important.
"Dude, you ever like a friend more than just a friend and not know what to do?" if he says yes.. then say.. "okay.. how do I handle liking you more?" then laugh. If he likes you back.. he will be "awww.." if not.. you can say you were joking.. and get out of it easily.