Search a large enough area and you'll find some vaguely plane-like fuzzy shape. It "could" be the plane, but I bet there's a good chance it will turn out to be something random.
how a whole plane vanish without a trace
World is a big place. This happens pretty often actually.
Remember that rugby team that crashed in the Andes? White plane on White snow at high elevation in the middle of nowhere? They were there for ten weeks and the search had been given up, if it hadn't been for the ones that finally hiked out on their own, who knows how many years it would have been before someone found that plane.
Vickers 785D Viscount disappeared off Ecuador in 1976, wasn't found until 1998 when melting glaciers allowed it to become visible. Merpati Nusantara 6715 disappeared in bad weather near Indonesia in 1995 and has never been found. And just two years ago in 2016 an Indian Air Force An-32 disappeared over the Bay of Bengal and hasn't been found. Those were both good-sized planes. EgyptAir flight MS804 was a big passenger plane that disappeared in 2016 and took about four weeks to find.
these airlines are too cheap to lojack their own planes
Modern planes send out their GPS location twice a second, but it can only be received if you're in line-of-sight, and there are places over the ocean or in remote land areas that have no receivers line of sight. And that requires an antennae to send the signal, which is the sort of thing that gets destroyed in a serious crash.
There's also an underwater pinger that sends a sonic signal, but you pretty much need to be in the water or very close to locate it, the signal doesn't travel far in air.
the truth is far more sinister