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. Thai police and Interpol questioned the proprietors of a travel agency in the resort town of Pattaya that sold one-way tickets to two men now known to have been traveling on flight MH370 using stolen passports.

Malaysia’s Department of Civil Aviation chief, Azharuddin Abdul Rahman, told a news conference that investigators were looking at “every angle” to explain the plane’s disappearance early Saturday, including hijacking.

“There are many experts around the world who have contributed their knowhow and knowledge,” Azharuddin said. “As far as we are concerned, we are equally puzzled as well.”

The search operation has involved 34 aircraft and 40 ships from several countries covering a 50-nautical mile radius from the point the plane vanished from radar screens between Malaysia and Vietnam, he said.

Experts say possible causes of the apparent crash include an explosion, catastrophic engine failure, terrorist attack, extreme turbulence, or pilot error or even suicide.

Selamat Omar, a Malaysian whose 29-year-old son Mohamad Khairul Amri Selamat was a passenger on the flight, expected a call from him at the 6.30 a.m. arrival time. Instead he got a call from the airline to say the plane was missing.

“We accept God’s will. Whether he is found alive or dead, we surrender to Allah,” Selamat said.

There have been a few glimmers of hope, but so far no trace of the plane has been found.

On Sunday afternoon, a Vietnamese plane spotted a rectangular object that was thought to be one of the missing plane’s doors, but ships working through the night could not locate it. Then on Monday, a Singaporean search plane spotted a yellow object some 140 kilometers (87 miles) southwest of Tho Chu island, but it turned out to be some sea trash.

Malaysian maritime officials found some oil slicks in the South China Sea and have sent a sample to a lab to see if it came from the plane.