Well if it's at the fault of the person who entered the giveaway, I would say that would be totally fine. Just ask for a re-roll, and state your situation.

Why not send it to their email?

Send it to the winner's email first.

Send an email letting them know they won, and to accept your fiend request so you can send the game over Steam chat.

I would wait the entire 7 days, then ask for a reroll. In all honesty, can't you just post a comment or something on their profile?

(Unless it's private. Happened to me once, only the guy didn't have the base game...)

That would be unfair....send him the game by email he provided as stated in the rules what you should do to make it fair

Don't send it to their email. If I were you I'll ask for a reroll.

After all he's the winner he should be the one caring. If he doesn't, it's his problem not yours. Ask for a rerol.

E-mail them to tell them they've won. If they don't reply after that, you can then reroll after seven days.

I'm having the same issue with 2 of my giveaways, it states I will contact via steam. I fully intend to wait a week then request re-roll. I made it fair by stating I would contact winner via steam. If the guy hasn't made the effort to accept a friend request and/or respond within a week then he doesn't deserve the free game I am offering.

If the winner can't bother accepting friend requests for 7 days despite being online, a screenshot of the invite and a week later, it's a reroll request if you ask me... The giveaway creator shouldn't have to jump through hoops to gift a game. Of course jade's is again the voice of reason (ie an e-mail reminder won't hurt), but I'm just guessing your winner won't bother answering even after a quick e-mail.

From the FAQ

The submitter and winner(s) of the giveaway have seven (7) days to complete the gifting process.

Why do you work so hard to get the guy to accept it? If he's ignoring your requests, screw him. Too many ungrateful wretches on Steamgifts. Re-roll and give to someone more deserving and appreciative of your contribution.

He got my email and the gift while I was sleeping. Now I'm just waiting for him to register it as recieved.

The rules say "The giveaway creator has 1 week to email it before you can mark the gift as 'Not received'." When you win a giveaway, the site tells you to check your email and mark the gift as received once you find it in your email. It seems pretty clear that you would be breaking the rules by not attempting to send it to him by email. (I see you sent it to him by email now, but I just wanted to explain what I think the answer to your original question is.)

As stated above, you might try to email the winner to let him know you added him to steam to give him the key if that is the way you prefer to use to proceed.

Same happened to me with my last giveaway, I'm pretty new to this, as was the winner himself, he just nicely emailed me back and accepted the invite. Not knowing why, I would barely accept myself random invites(but would wonder about steamgifts if that happens from now on, that said, I'm pretty confident I won't ever win but lotteries are fun).

Might be just circumstances and we are all busy at times (add to that I let my comp run, browser and steam even in game, just a bad habit, but my played time really means nothing... 110 hrs in dead island the past week for the history, I'm in the end of the act II... Seriously, nobody can be that bad it would take that long to reach that point side quests included :D).
As long as the 7 days delay is going, no need to go to the extreme nor be worried, just do your best to contact the concerned person.