My iPhone was stolen, what can I do to protect my data and get the phone back?
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.
Provided you have Find My iPhone enabled, you can go to iCloud.com and lock the device and locate it on a map. If the phone is not on when you find it, it will alert you when it is turned on and located. Once you know where it is, you can get it or have the police get it, depending on the situation.
Besides that, I'd recommend calling Apple at 1-800-MYAPPLE and seeing if they can help you disassociate it from your Apple account, and you can report it to your cell carrier so the phone will be disabled permanently.