In response to replies 4291 and 4292.
Even in the aircraft (or at least it's mayor components) was intact at impact as the preliminary analysis of the BEA let to believe, it will most likely have broken into pieces at impact. Even if such a piece could be some 20 m long, it is still very difficult to find.
Immagine a surface of the size and shape of the 'Haute Savoie' (that's where the Mont Blanc is) with every mountain being quite similarly high like the Mont Blanc, some 2 km of water on top of that and the necessity to sweep through every single valley to find something, provided the something is not hidden by an obstruction like an overhang or similar.
In an unpopulated region such a search over normal land can already yield into the complete loss of an aircraft only to be found by very lucky circumstances. Water just maked the whole thing 100 times more difficult.