The boat had been carrying mostly students returning to southern Myeik city after a two-week break when it went down on Sunday.
Eleven bodies had been recovered as of Monday.
Rescuers found “eight more dead bodies today, including three children,” a resident of Kyauk Kar village, where the boat had set out, told AFP on Tuesday.
The five others were students aged between 18 and 20, he said, asking for anonymity to talk to the press.
Local media reported around 60 people had been rescued and eight were still missing.
Boat accidents are common in Myanmar, a country with rudimentary transport and weakly enforced safety regulations.
Vessels ferrying people along the coastline and rivers are often dangerously overcrowded, and accidents can have staggering death tolls. It can also take several days for all bodies to be retrieved.