Exactly How Does a Plane Dissappear?

I have been amazed at the lack inability to locate the downed jet with 228 passengers on board?! The news says it "probably" crashed into the Atlantic, but they don't really know for sure. Don't these major jets have flight plans and things like that? Blackboxes? Pretty much anything to keep them from falling off the face of the earth?! If they find the plane on an island with polar bears I will not be surprised!