What should I do after my iPhone was stolen?
Sorry to hear that, but if you have your iPhone setup with iCloud then most likely you have Find my iPhone setup and by following these instructions you'll be able to place your phone in Lost Mode and that person won't be able to view any of your content and if you have iOS version 7.0 (which you do, as the iPhone 5s shipped with iOS 7) or later then the phone will have an Activation Lock meaning that this person could never activate this iPhone even if they place the device into DFU mode.