If it locates your device, Find My iPhone zooms in on the map and shows the location of the device using a green dot. When this happens, you can zoom in or out of the map, and view it in standard, satellite, and hybrid modes, like in Google Maps. When your device is found, a window appears in the right corner of your web browser. It lets you know how much battery your phone has and offers a few options.
Click Play Sound. This is the first option because sending a sound to the device is best when you think you've lost your device nearby and want help finding it. It can also be helpful if you think someone has your device but is denying it.
You can also click Lost Mode. This allows you to remotely lock the device's screen and set a passcode (even if you hadn't previously set up a passcode). This prevents a thief from using your device or accessing your personal data.
Once you click the Lost Mode button, enter the passcode you want to use. If you already have a passcode on the device, that code will be used. You can also enter a phone number where the person who has the device can reach you (this is optional; you may not want to share this information if it's been stolen). You also have the option to write a message that is displayed on the device's screen.