Cellphone Monitoring
It seems the US can track cellphones from drones, likely based in Diego Garcia, and occasionally dispatches a Hellfire to a target identified from a drone and/or satellite.
Perhaps a number of cellphone pings were picked up and associated with the errant flight.
We can expect that any information derived from such activities will be carefully sanitised.
The destroyer sent out on the track most likely has at least one helicopter equipped for searching the ocean surface and underneath.