The two passengers with stolen passports have been identified, but the identities and nationalities are being shared only with intelligence agencies
Why? to prevent mass panic when the public discovers that this is just phase one of North Korea's master plan:
North Korean operatives using stolen passports board the plane with the technology to jam all of the planes communications
Jam the plane, hijack it without a distress signal
Land in one of Vietnam's many (many) abandoned airports leftover from the Vietnam War. Or possibly Cambodia, it was very close to both when it disappeared.
Hold all passengers hostage or just kill them, take on fuel
North Korea has decent-sized nuclear warheads but no reliable intercontinental delivery systems. The solution? steal an airliner, use it to carry warheads.
In a few days, or weeks, the mystery airliner (with transmissions still jammed) takes off, headed for Seoul or another huge international city
Worst terror attack in the history of the world.
Maybe it will happen on April 15, to mark the birthday of Kim Il-Sung, eternal president of Korea
Source - Reddit. Before it vanished from the site when i went to get the link