Just throwing this out there...
In the crash of MI185 at Palembang of a 737 in 19 Dec 1997, the crash site had very little debris. The aircraft apparently went into a steep dive and plunged into the palembang river. There were some debris that were on the surface (due to the inflight breakup) and surrounding dry land but at the impact area, most of it went straight into the riverbed due to the immense speed. Pilot suicide was concluded by the NTSB but the Indonesian government official report could not definitively state it as a concrete finding. A group of families took their own action to sue the manufacturer of a part which commands the rudder and was awarded some settlement (in USA courts). The vid is available on youtube.
If there is anything to take from this incident, it would be that the high speed of impact will leave few floating debris. Any that were generated during the breakup would be scattered over a wide area and very difficult to find (compared to a narrow river). As for the lack of comms and silence in the cockpit, apparently the MI185 incident captain had a history of disabling the CB to the CVR which was NTSB's key link to the suicide theory. Though investigators also revealed that there was a history of problems with the power to the Black boxes in the preceding flights.
Really hope to find out what happened soon so that the families can get some closure.