Microsoft co-founder Paul Allen's mega-yacht is part of a flotilla scouring the Pacific for an American pilot and two Palau police officers whose plane disappeared over the weekend.
The plane vanished Sunday as its crew was helping investigate the alleged poaching of giant clams from a marine reserve by a Chinese vessel.
A crew member of the vessel was shot and killed by Palau authorities in a confrontation on Saturday. Allen's 414-foot yacht, the Octopus, has two helicopters, a submarine and a remote-controlled underwater vessel.
The Coast Guard said it wasn't clear if Allen was still on board. Allen's spokesman David Postman said Allen had been in the region to support his friend, film director James Cameron, who recently explored the world's deepest point, the Mariana Trench northeast of Palau.