How do you find a Stolen iPhone by phone number?

How do you find a Stolen iPhone with its phone number? Can you Still track the phone device itself, if it’s Activated , with just its phone number?

Law enforcement or maybe even the Phone provider should have a way of doing so, especially the Phone provider. Can somebody explain any options if It was NOT registered or was Activated with “FIND MY PHONE” App?!? Thanks to any who can help answer or provide assistance with this.

Gratzi