How do i find my iPhone if it’s off

If you enabled the Find My Network feature before it was lost, for a short while after it is turned off it may be located through crowd-sourced reports. Go to https://icloud.com/find, and if it has been located by another iPhone you will be able to see its location. Other than that you will just have to use “traditional” location methods, such as retracing your route and looking in places you have been.

Go to the last place you remember having it and look for it. If it's not there, retrace your steps, looking along the way.