Can we find the buyer of iPhone with IMEI number?

Sorry, that’s not possible for you. If it was used in a serious crime law enforcement could get a warrant request to registered information from the carriers in a given area, but if it had a PAYG SIM card that would be an impediment.

Apple does not use the IMEI number to locate an iPhone.

If your iPhone or iPad is lost or stolen - Apple Support

In theory.....yes. In practice......no.

But, you would need to know the carrier that the phone is locked to.....and.....the carrier would have to be willing to divulge private personal details.

The carrier would never do this of course, unless you presented them with a court order.

This is my phone i need IMEI number please 🥺 my phone is lost