Back a few years when I did it we relied on our eyes and binocs only.We were trained in tequniques for scanning the surface and CG District 7 knows the seas winds and currents and sets up the search patterns.
Electronic buoys were dropped to measure currents and aid the process.
I am sure with technology things have gotten better but its still the old needle in a haystack scenario.
I can tell you after a day or so and you do find something or some one it is a thrill.
I did read a little bit about determining likely position using software and working from that, but beyond that I have no idea. I spend a little time on the water, I have a strobe and a marine transceiver clipped to my PFD and want to get a couple of smoke floats. Maybe something for hydration, as well.