Patience will be rewarded.
Having crossed the Atlantic and other seas several times by ship, I can only say that I found it virtually impossible to see anything of note from that level other than the "white horses" of the wave tops and occasional algae so the SAR ships may be more concerned with picking up bleeps than visual clues. But I accept they will be trained in what they're doing so let's leave them to it.
Similarly looking down on the Atlantic (North / South / Mid) from 35,000 feet I've never seen a single yacht, container ship, tanker or cruise ship - and only occasionally another aircraft - in dozens of flights. Maybe I'm unlucky but the seas are awfully large and empty places, the South China Sea included, so you have to hand it to the Chinese if they have discovered something significant from satellite images. For the families' sakes I hope this is some concrete news.
Having spent thousands of hours flying maritime patrol and SAR I can tell you that you can see a lot more from 1000' and below.