He should have received an email to the account that you sent the gift to, with redemtpion info about the gift (he's checked the spam folder on that account as well as the inbox ?).
You could try resending it : http://support.apple.com/kb/HT1541
If that doesn't arrive either then try the 'report a problem' page to contact iTunes Support (I'm not 100% sure if gifts will show there) : http://reportaproblem.apple.com
If the 'report a problem' link doesn't work then you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption