IMEI number formy lost iphone

1. Go to account.apple.com in a web browser.
2. Sign in to the Apple Account that you use on your device. 
3. Choose the Devices section. To see the serial number, EID, and IMEI/MEID, select the device.

Find the serial number, EID, or IMEI on your iPhone, iPad, or iPod touch - Apple Support

Not sure how you are attempting to trace it with the IMEI number, but make sure you are not being scammed by someone making that claim.

The only way you can track your lost iPhone is with Find My. Only your carrier can track your iPhone with the IMEI number, and they will only do so with a court order or when someone's life is in imminent danger.

Please review the article below:

Find your lost iPhone or iPad - Apple Support

Apple does not use IMEI to track a phone.

If you still have the original box that the iPhone came in, the Serial Number and IMEI are on a label on the box.

Your carrier should have the IMEI in their records.

Click here and see the last section.

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