...yet after an extensive day's searching ... mysteriously no debris has been sighted...
Nothing mysterious, neither surprising. Communications was lost in the small hours, with ETA at 6am with an extra 2 hours endurance. In the first hours after loss of comms, an increasingly frantic exchange of messages with neifhboring FIRs. It probably took a good 3-4 hours until the grim reality started to sink in, and somebody plucked the courage to wake the CEO. It probably took another couple of hours to establish with a reasonable degree of confidence where to start looking (there was quite a bit of confusion at the beginning on exactly how far into the flight was communications lost).
All the involved countries are fairly rigid hierarchical societies, which means information must be passed up the chain of command, then down again on the other end. This is complicated by the disputed territorial claims on various parts of he South China sea, which means that the SAR process must have had to been coordinated an an unusually high level. I doubt that the actual search would have been launched before late morning, midday, with 5-6 hours of daylight left. Probably there were no more than a couple of sorties flown over a vague target area before it became dark. Daylight tomorrow will hopeful bring results, as the search can get better organized tonight, with well defined areas and responsibilities for participating aircraft and vessels. Remember that the first AF447 wreckage was only spotted 2 days later. Then we had the ACARS messages to chew on, while now if they do exist (probably they do, as all Malaysian gov't and airline officials seem to accept the total loss as fact) they are not in the public domain.