find my device dosent work

Assuming that you enabled the Find My feature on the phone......before....it was lost, the following things need to be in place:

1) The battery needs to have a good charge

2) The phone must have an Internet connection

If either of these two things are not working, then the phone will show as "Offline" or it will not show up at all. All that you can do is keep trying to see if the phone will appear.

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

Try the steps in this article:

If Find My is offline or not working - Apple Support