In order to obtain the title, you must pay the lender in full. So, even if you did find someone willing to purchase your car for $12K (very highly unlikely), you'd have to pay off the loan before you could request the title.
Don't try to sell the car for less than what you owe. You will have to come up with the cash difference in order to satisfy the note. If the buyer tried to register the car in their name, they couldn't do it. Then, a whole world of trouble ensues upon you.
Honestly? Keep paying on it, try to double-up as often as you can. There is no easy way to get rid of negative equity. Millions of Americans are in your shoes right now due to the economic crunch that the car business is feeling. Resale values are dropping like crazy, and it's affecting everyone.