From what I've been reading if it was an illegally obtained copy you are most likely out of luck. Read this post from the steamgameswap subreddit. It might be of some help.
http://www.reddit.com/r/SteamGameSwap/comments/1m07v7/psa_advice_on_revoked_games_and_information/
1 decade ago
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New Bundles
Hey I traded with a guy a few days ago, exchanged gifts. Today I checked inventory and gift of Don't Starve is no longer in my inventory. I tried to contact that guy that was the source of that gift and it turns out he is a scammer, he has a trade ban now. I asked him if his gift was stolen and he said "no are you kidding". I think he stole it though and support gave it back to the original owner. How do I get my gift that I gave to the scammer back ? I don't have a proof that his gift was stolen but support took it for some reason. Please do I need screenshots, or any other evidence? Please more experienced guys answer my question.