A lot depends on the marine search capabilities in the area. Beijing has the resources, but whether the Vietnamese want them in their waters is another question.
An aerial search may turn up debris; then you have to get a boat to pick it up.
Once debris is located, there will be a starting place to search for the pinger, but that equipment has to be brought in to the area.
Local fishermen might turn up something, but do they have radios?
Very few fishermen have radios. Vietnamese Coast Guard has state of the art, very capable fast oceangoing SAR vessels. Vung Tau, not far from where to a/c reportedly crashed, is the centre of the offshore industry in VN; lots of helicopters there, large anchor handling tugs/supply ships with equipment for salvage etc.