My iphone is stolen but my find my is offline

Assuming that you enabled Find My on the phone......before......it was lost, the phone will still show up as "offline" if it is not powered on, the battery has run down, or the phone does not have an Internet connection where it is currently located.

Technically, the phone is supposed to show up even if it is off, but this is a very "iffy" proposition that depends on another Apple device in close proximity to the lost phone.

There is not really anything that you can do at this point other than to keep checking every 3-4 hours to see if the status has changed from "offline".

Unfortunately, thieves usually power the phone off to prevent the owner from locating the phone. Again, not much that you can do about this.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

You did enable Find My on the phone.....before....it was lost, correct? If not, the phone will always appear as "offline".

The phone will appear on the Find My map if is has power and a connection to the Internet. That would mean that it would need to be connected to your cellular carrier's network at its current location.

If Find My iPhone is offline or not working, read this support article --> If Find My is offline or not working - Apple Support