The court reduced the previous sentence of six years imprisonment and THB30,000 fine, as they had pleaded guilty.
The court also suspended the imprisonment for a year per person as the partygoers did not have a criminal record.
Police had arrested 28 people, nine of them underage, for partying at a swanky resort in Bangkok’s Din Daeng district in the early hours of Wednesday.
The nine underage suspects will be charged separately by the Central Juvenile and Family Court.