I made a key giveaway, the winner keeps ignoring me

+1

I tried to add him already, he didn't accept the friendship invitation.

I can't, I don't own Skyrim. Got the key by accident.

And it was a group giveaway? lol, how horrid.

Yepp.

he is logged on steamgifts now :)

This.

Make sure you give keys through steam chat so that they understand and acknowledge the gift.

It doesn't really matter whether it's sent over e-mail or chat. Most keys I have sent and received have been through e-mail. In cases like this, while it can't be re-rolled (not because it was sent over e-mail but simply because it's a key), support can manually mark the giveaway as received. In fact, they often get requests like that. All they require is proof -- like a screenshot of the e-mail or chat window.

However, it seems that the winner already marked the game as received just recently so all of this advice (and the discussion itself) is moot (at least in this instance).

It'S the Skyrim Dawnguard DLC. Dunno if it's shown in the games list.