Be a lot simpler if the aircraft itself routinely transmitted a signal with location co-ordinates, that would generate an alarm if signals were not recieved at 'home'
Last signal = last known location = where to start looking.
You would also be able to work out speed and heading from the previous transmissions so you could search in the right area.
This might provide a better guide to finding the recorders than following floating wreckage and best guesses.