Wait for 7 days and write to support with screenshots

If you sent via e-mail, than it is possible it is in his spam folder. Or he forgot to mark. Try contacting him through Steam first, and after 7 days write support ticket with screenshots showing you sent link to the winner.

Is the game on the winner's Steam profile?
Has the link been redeemed? Click on it to check. If it's redeemed it will say so. If it's not it will ask you for an email address which might be auto filled in if you're logged in to humble bundle, just don't click redeem if you see a redeem button.

it won't help you resolve anything for certain, but those might be things you want to check if you're wondering what's going on.

This is why I always contact my winners by Steam chat. I like to confirm receipt of the gift in real time.

He might have connection problems/maintenance going on on his line or hasn't paid the internet bill and been disconnected, or something. The list of "He could"'s is a veritable cornucopia of reasons why he hasn't verified yet. As UraniumFalconPunch asked, has it been redeemed and is on his games list? He might have the email in Spam, depending on who your email supplier is and who his are, and hasn't seen the email.

I won game few days ago and havent received :/