Have you traded it for keys, money, game keys, ...? If you traded it for items on the trade window, Steam Support can get your items back.
Also, just a friendly advice: buy DayZ yourself or, if you wanna take a shot, at least look for trustable traders, which sells it for ~15 keys. Anything lower than this, as the price is almost the same everywhere, there's a high chance that you are gonna be scammed or getting the game revoked after a while, as you had now...
Also, please, let us know who sold you the game.
Hey, thanks for the quick response. I don't know. I've checked my steam trade history and all my trades are there except the one of dayz. And do you think "Yay, I love Pony!" was the person who's gift got stolen?
EDIT: I found him, I was an idiot and didn't look on my main account: http://gyazo.com/7ea1edf7ddd952dd9508c59841ee4768
Using this nick, I've found only this person: steamcommunity.com/profiles/76561198093060887. Did you got it from this guy? If so, I'm sorry to say that, but that's a quite shady profile and you should have suspected, as the game is quite expensive to risk money on offers 'too good to be true'...
Also, what did you offered to him? The trade was done through trade window (ie: game for TF2 keys)?
I found him, I'm an idiot and didn't look on my main account: http://gyazo.com/7ea1edf7ddd952dd9508c59841ee4768
I just talked to the guy who traded me it, he said that he got it off another trader. His the profile: http://steamcommunity.com/profiles/76561198049752495/
Maybe he can track this gift on his trade history as well, so you will be able to find who got this at first to report for fraudulent activities.
And, as you've traded all on trade window, follow the tips on this guide and create a ticket on Steam Support. If they reply with a stupid and generic copy/paste, send another until they get your items back. They can, but they will bitch a lot before giving something back to you, if you don't find someone in his good mood for this...
Talking to him now. He told me that he got DayZ from 2 different people.
http://gyazo.com/5a2a610856617f51b4b737513a66d832
The two peoples steam profiles:
http://steamcommunity.com/profiles/76561197994788939
you buyed a stolen DayZ, because it you need find a good seller, who buy with his steam wallet, like me and others.
you can send a message to Steam support, they can refund you, but they do it only 1 time in your life, if you get hacked and lost all yors itens you never more will be refunded. If you buy another stolen game steam won't refund you too.
post the profile from guy you have buyed it, to people take care with him, and support can ban him from steam trades.
I logged on to my account today, and got this message: http://gyazo.com/b0b7e2a90c3e3ffd9a6923a29d12bb61
I'm so pissed, I've played over 40 hours of DayZ.
Any way to fix this?