Apple has come with built in feature to locate your iPhone if it is stolen. Here is how we set it.
Go to Settings > [your name] > Find My, tap Find My iPhone, then turn on Find My iPhone. You can see the location of your devices in the Find My app 
. If you lose your iPhone and don’t have access to the Find My app, you can locate your device using Find iPhone on iCloud.com.
Source : Apple Support
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