Sorry, It's Gone
Use FlightRadar24 and playback starting at about 17:15 UTC. MAS370 is the one sorta midway between Malaysia and the closest part of Vietnam. Its at 35,000 on heading 25 until 17:19 (01:19 local), then it goes to zero feet. Radar coverage is good in the area.
Where the plane is (generally) is not the question. What caused it to get there is the question. Sorry. That plane is not on the ground anywhere.
Also, airlines don't call next of kin if they think there's any hope.