I left my iPad in a seat back, was able to activate "find my iPad" before it went dead, and "found" it in the SEA US lost and found. Called and it was returned to me.

If you do not have the "find" option, suggest you call the airline, determine the route of the plane, and call each lost and found along the flight path.

Note to all - ACTIVATE THE FIND MY IPAD-IPOD-IPHONE-I whatever.. They work.