Well if you consider that they knew the plane was at "X" when it was last radar identified and then it had 5.5 hours more fuel on board. Some quick math reveals that the plane could be anywhere inside a circle with a radius of say 2500 miles or about 19.5 million square miles of mostly water.

Unless the theory that the plane was "stolen" and flown to an airfield for a later "nefarious" purpose (reportedly a favorite theory of the US military at this point), the chances of ever finding this plane are approaching NIL.

PS. Happy Pi Day!