Does anybody know Gabe Newell's email ?

Have you used the trade window? Have you proof he scammed you? This is seriously not a reason to E-Mail Gabe Newell. And since support rarely does anything the "scammer" framing you has no effect all. Well, if he has proof that you did something illegal it is another story. But you have nothing to worry about, do you?

Provide a ticket with screenshots and trade time so they can trace back the transaction. Newell won't do anything about this unless you have enough claims to prove your plea. Also, I hope you provided all these evidence to SteamRep too, because it is the foremost tool people use when trading to check real reputation and also to check for impersonators.