I need to find my son's iPhone to find his location

Contact the police. They can have a judge issue a court order to the cellular carriers to track the device using the IMEI.

That's your only option if he has not actively shared his location with you.

Please notify the police immediately.

Hopefully, Find My was enabled on the phone.....and.....you know the Apple ID and Password for the phone.

Find your lost iPhone or iPad with Find My - Apple Support

If you know the carrier that was being used on the phone, contact them to ask for help as well.