Just google it. Start with some where know of that you would like to visit and go from there.

12 days won’t get you enough time to see even a quarter of some of the main “tourist spots” in America. America is bigger than Australia – size of the USA 9.827 million km², size of Australia 7.692 million km². If you only spend 12 days there, you’ll end up spending a lot of the time flying on planes from one place to another, and very little time actually seeing the sights. It would be like traveling around Australia, and spending 1 day in Perth, 1 at Ayer’s Rock, 1 in Adelaide, 1 in Melbourne, 1 in Tasmania, 1 in Sydney, 1 in Brisbane, 1 on the Gold Coast, 1 on the Great Barrier Reef, 1 in Darwin, etc. There are so many more cities and sights to see in America than in Australia. If I were you, I’d consider either spending longer away if you can afford it, or concentrate on only a few sights in America for this trip.