Deleted

As far as I know there are no means for private messages on this site. Look up his steam profile or email if simply commenting does not work!

You can try to comment on their Steam wall or add them as friend on Steam, but the comment in the giveaway should be sufficient.If there is no reply by the giveaway's creator within a week, just mark the giveaway "not received".

No.

You have done all.
Wait.
If nothing happen till the 7th day, then mark it as not recieved.

exactly what oppenh4imer and masafor have said. when you comment on their giveaway page, they receive a notice on here that's akin to any notice that would be received simultaneously with a private message. it will simply be at the top of their messages page. if they don't see that, then they ostensibly wouldn't see a private message notice either. it's their responsibility to send you a proper working key after the giveaway, and if that isn't met then you should feel no guilt about marking it not received 7 days after the giveaway ends. it's also worth noting that just because a giveaway is marked as such doesn't mean that's permanent. they could always get back to you any time after to rectify the problem by giving you a proper key for the game you won, or some other mutual agreement. i have a won giveaway from 10 months ago i've marked as not received yet i still have the option to change it to received.