When you discover that your iPhone has been stolen, dozens of thoughts race through your head all at once. Anger, worry, surprise are all likely to pop up. Once they pass, though, there are some steps you should take. While there's no guarantee that these steps will get your iPhone back, they won't hurt and will succeed in some cases. Good luck.
1. File a Police Report
File a report with the police in the city where the phone was stolen. This may or may not directly lead to the recovery of your phone, but having documentation of the theft may help in dealing with cell phone and insurance companies and, if you can get data about the location of your phone, having the police report on file may be necessary for getting the police to help you recover it.
2. Notify Your Employer
If your iPhone was issued to you through work, notify your employer of the theft immediately. In that situation, you may even want to do this prior to filing the police report, since your corporate IT department may be able to prevent the thief from accessing critical business information. Your employer may have given you guidelines about what to do in case of theft when they issued the phone to you. It's a good idea to brush up on them.
3. Change Your Passwords
Don't let the thief gain access to other accounts whose passwords may be saved on your iPhone. Changing your email account passwords will prevent the thief from sending mail from your phone. Additionally, changing online banking, iTunes, and other important account passwords will prevent identity theft or financial theft.
There are a number of ways to use the iPhone's built-in GPS to track a stolen iPhone. Apple's free Find My iPhone service (the link above takes you to more information about it) and many third-party apps from the App Store will help you locate the phone geographically. Getting this data can be crucial for recovering the phone. Some of these apps, including Find My iPhone, also allow you to remotely change security settings (more on this below).
Related: Why Is Find My iPhone Not Working?
5. Call Your Cell Phone Company
Making this the fifth step in the process, or an earlier one, will depend on your circumstances. Some cell phone company representatives may be more inclined to take action when you've got a police report, others may act right away without one. Calling your cell phone company to report the theft and have the account tied to the phone suspended or canceled will help ensure that you're not stuck paying for charges incurred by the thief. Try tracking the phone first, though, since cancelled service could make tracking it hard.
6. Don't Try to Recover It Yourself; Get Police Help
If you've been able to locate your iPhone via a GPS-based tracking app, don't try to recover it yourself. Going to the house of the person who stole your phone is a certain recipe for trouble. Instead, contact the police department you filed the report with, make sure to have your report information at hand, and let them know that you've got additional information about the location of the stolen phone. The police ought to be willing to recover the phone for you.
7. Delete Data
If you can't get the iPhone back, or it's taking too long, you may want to delete the phone's data. You can do this over the web using iCloud or some of the other tracking apps. This won't prevent the thief from using your iPhone, but at least they won't have access to your personal data after that.
If your iPhone was issued to you by your employer, your IT department may be able to remotely delete the data, too. Contact them to learn about your options.
If you're using a third-party insurance company to protect your iPhone, and your policy covers theft, be sure to call the company. Having a police report will be a big help here. If you can recover the phone with the help of the police all the better, but reporting the situation to the insurance company will get the ball rolling in the meantime and help you replace your phone if you can't recover it.
9. Notify People
If your phone's gone and you weren't able to track it via GPS and/or delete its data, you're probably not going to get it back. In that case, you should notify the people in your address book and email accounts of the theft. They probably won't be getting calls or emails from the thief, but in case the thief has a bad sense of humor, you'll want people to know that it's not you sending them troublemaking emails.