Indeed the main complaint from relatives of the plane's passengers is lack of information, and lack of updates. It's of course a tough situation - they don't really know anything, a plane disappears without distress call in good weather, and then there is no wreckage or anything to be found. So yes, the pressure is immense to come with new information. Any new information.
It's indeed quite sure the people on board are dead. And I'm also quite sure the plane landed in the sea, not on land, as in the second case not only is debris much easier to spot - big plane, lots of debris, also very likely someone would have seen the fireball of the plane crashing into the ground. A hijacker flying the plane until it has run dry (preventing a fireball) is extremely unlikely; hijackers normally are not suicidal and will try to go somewhere the plane was not supposed to go, in the process informing air traffic control of the new flight path.