Malaysia Airlines Flight 370 took off from Kuala Lumpur shortly before 1 a.m. Saturday (12 p.m. Friday ET). The plane disappeared somewhere between Malaysia and Vietnam. Since the disappearance, teams of searchers from Vietnam, China, Singapore, Indonesia, the United States, Thailand, Australia, the Philippines and New Zealand have been working alongside Malaysians to scour the Gulf of Thailand, part of the South China Sea ,that lies between several southeast Asian countries.

Nearly three dozen aircraft and 40 ships from 10 countries have been out searching the larger portion of the Gulf of Thailand between Malaysia and Vietnam for the missing flight 370. As they begin day four of the search, there is still no sign of flight 370. “Now it’s a search area hundreds of miles big,” Cmdr. William Marks of the U.S. Navy 7th Fleet told CNN. No emergency signal has been detected by any search vessel or aircraft.

Two men who boarded the airplane with stolen passports, and the man who bought their tickets have become high focus for the ongoing investigation. So far, authorities have not said why these men were on the flight, or who they were.

Family members are being told to prepare for the worst, for it is too soon to know why the plane disappeared. Investigators are weighing a number of possibilities, and nothing is being ruled out. Although terrorism is still one of those options, investigators are saying it is looking less likely.