There's not much you can do. Although you can lodge a complaint with the tourism police, pickpocketing tends not to leave a lot clues to go on. If you do, make sure you bring a turkish friend, as the cops are unlikely to speak english. Your best bet is to CANCEL YOUR CREDIT CARDS (if they got stolen), and ask your bank what the best way to get money for the rest of your trip is- some banks in the states have sister banks here. If your passport was stolen, go immediately to the US consulate, and have them help you make a complaint.
To prevent pickpocketing again, it's best to keep your wallet and important things in your front pockets or inside your jacket. When you are in crowded areas, don't be afraid to keep your hands around the area, and be cautious about any bumps from strangers.
Sorry you got pickpocketed, hope the rest of your trip works (or worked) out!