KUALA LUMPUR, Malaysia — Rescue helicopters and ships searching for a Malaysia Airlines jet rushed Monday to investigate a yellow object that looked like a life raft. It turned out to be moss-covered trash floating in the ocean, once again dashing hopes after more than two days of fruitless search for the plane that disappeared en route to Beijing with 239 people on board. With no confirmation that the Boeing 777 had crashed, hundreds of distraught relatives waited anxiously for any news.