The majority of child sex offences in the region are perpetrated by Asians, not Western tourists, according to the United Nations Office on Drugs and Crime (UNODC).
A report by the regional branch of the office has claimed that Asian offenders are becoming prolific, while the integration of the Asean Economic Community (AEC) next year will bring even bigger risks to children.
Jeremy Douglas, regional representative for the UNODC, said soft border restrictions between countries will make it easier for perpetrators to travel.
Intelligence indicates that a new child sex tourism industry is emerging in Myanmar since it became easier for visitors from within and outside Asia to visit the country, Mr Douglas said.
Evidence of how tourism corresponds with increases in child sexual exploitation suggests that many more young victims will be at risk as the region continues to develop, he added.
Total tourist arrivals into Asean are also projected to rise from 40 million in 2014 to 112 million by 2018.
The "Protecting the Future: Improving the Response to Child Sex Offending in Southeast Asia" report has not been released to the public but is being used to in regional police officers' training.
Mr Douglas said Caucasian males are seen as the stereotypical child sex offender, but studies show the number of Asian tourists who engage in child sexual exploitation outnumbered Western child sex offenders over the past year.
According to a 10-year survey carried out between 2003 and 2013, Japanese criminals carried out the most offences among foreign Asian perpetrators in Thailand.
Criminals from Britain accounted for 30% of child sex offences carried out by foreigners in Thailand, closely followed by those from the United States and Germany.
Mr Douglas said regional authorities are currently failing to effectively share information about child sex offenders, while there are too many loopholes in the judicial process.
The UNODC official argued that a database of child sex offenders must be established to alert immigrations officials and stop criminals from crossing borders.
He cited the recent example of a Canadian child sex offender who served several years in a Thai prison but was sent back to Canada, despite being wanted for child sex crimes in Cambodia.
Mr Douglas added that corruption at all levels facilitates the crime, because predators bribe police and poor families.
"Our training workshops have interviewed police officers in the region. They admit that de facto corruption has caused the failure of investigations into child sex crimes," he said.
Margaret Akullo, UNODC programme coordinator, said UNODC plans to train law enforcement officials are only the beginning of an effective response to the issue.
One thousand police officers have been trained by the organisation already and 3,000 more are in line. But the number is still small compared with the millions of police officers operating in the region, she said.