Lost iPhone

Click on this link for general information about what to do "If your iPhone, iPad, or iPod touch is lost or stolen" --> https://support.apple.com/HT201472

If Find My iPhone is offline or not working' Click on the link to 'Get help when you don't see your device listed, or you see an unexpected device or an alert that says your device is offline.' --> https://support.apple.com/HT204233

Click here for information; in addition, post notices around where you lost it, and if applicable, contact the Lost & Found department of the facility where you lost it.

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If it is off line, there is no way to track it. Report it lost to the police and your carrier. See here too: https://support.apple.com/en-us/HT201472