Can you turn on find my device after it’s lost

Here is Apple’s advice for lost or stolen devices:

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

Use the Find My app to locate a lost or stolen device – Apple Support

Facilities to manage/recover a lost or stolen device are predicated on Find My iPad being enabled on the device before it was lost. Similarly, a device backup can only be created before disaster strikes.

deserae16 Said:

"Can I turn on the find my device from another device after the missing device is lost?"

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No.

So, do it the old fashioned way, by backtracking your locations, and contacting whoever may have come across it.