0.12 BTC is around $50 right now, this is small claims territory and depending on where you live it might cost you as much or more to file a suit to recoup your 0.12 BTC. You cannot escalate it past small claims in superior court as it is not worth more than the maximum small claims suit amount (usually somewhere between $1000 and $3500 depending on your state/district) I can tell you right now, if you get an attorney you will spend more than what you would get in return. It would likely just be better for you to wipe your hands of GPUCoin and mine something else.
We all understand you are upset, but constantly stating this on a forum that the owner of the coin doesn't frequent too often isn't going to help you. Sometimes, like a broken marriage, it is better to just walk away and chalk things up to a life lesson learned.
Also, the owner does not have to disclose anything, it isn't a publicly held company on the stock market.
A better plan would be to keep mining, tell everyone to buy the coin, use your time and knowledge of the internet to promote the coin, and then when it goes up, you will make way more than your IPO money back. And if you have been reading here, you will know that in about a week or so the blocks will half to 10,000, so your coins will be worth double and hopefully we can get known by then.
P.S. DID EVERYBODY DOWNLOAD THE NEW WALLET SO WE WON'T GET FORKED AND F@CKED WHEN THE BLOCKS DECREASE?