Originally Posted by training wheels
Quite possible, but switching your transponder off, you may still appear on primary radar returns if you're in radar range, but as an unidentified blip.
I'd add that it would require some detailed knowledge of the surveillance properties of a large area of airspace, and where could one take a 777 that wouldn't be noticed?
For my tuppence I think SAR seems like a long and very painstaking process, and it's incompatible with rolling news and social media.
They'll find it. It just may take a while.