A total of 12 Hongkongers had been detained against their will and at least two of them held for ransom so far this year after they were conned into flying to Southeast Asian countries in employment fraud and internet love scams, an emerging crime trend that has sparked a pledge from the central government to protect the city’s residents overseas.

A source on Wednesday said one family was forced to pay a large ransom to secure the release of a man lured to Thailand to meet his online “girlfriend”.

“He was released and returned to Hong Kong earlier this month after a ransom involving tens of thousands of Hong Kong dollars was paid,” the source said.

The 28-year-old was abducted in Thailand in mid-July and held in Myanmar until the ransom was handed over.

The news came as the Immigration Department said it had received 17 requests for help since January from families of Hong Kong residents feared to have gone missing in Thailand, Myanmar, Cambodia and Laos.

Department officials said 12 of the 17 Hongkongers had safely left the countries involved and they promised to work with the city’s police, the Office of the Commissioner of China’s Ministry of Foreign Affairs in Hong Kong and Chinese embassies and consulates abroad to help trace and return the five people still not accounted for.

It is not clear if the 12 cases revealed by police were among the 17 mentioned by the department.

Police said officers would liaise with overseas law enforcement agencies through Interpol to share intelligence and assist with the investigations.

The foreign ministry’s office said it made every effort to safeguard Hongkongers abroad.

“The office is in close contact with the Immigration Department and the relevant embassies … in actively searching for the whereabouts of the missing persons. We will continue to … follow up on the progress of the case,” a spokesman said.

He noted Chinese authorities had reminded people in February to exercise caution if they travelled to the north of Myanmar because of the security situation in the country.

Another case involved a 22-year-old man, also kidnapped in Myanmar.

The incident was reported to police on July 18 by the man’s father, 65, who said he had been able to talk to his son.

Another source said the 22-year-old was later freed, but it was not known if a ransom was paid.

Police have warned the public over potentially fraudulent online job advertisements.

The crimes sparked calls for a crackdown on job and romance-related scams by the Hong Kong authorities in partnership with overseas agencies.

Lawmaker Lai Tung-kwok, a former immigration and security chief, said international cooperation and public warnings about scams should be increased.

“Through international cooperation, similar syndicates have been eliminated in the Philippines, he said. “I’m sure the Chinese embassies in these countries are also trying to help, that’s why 12 victims have already left.”

Lai said the city’s legislative framework already had various legal provisions designed to combat people trafficking.

Matt Friedman, chief executive officer of the Mekong Club, a Hong Kong-based anti-slavery non-profit organisation, said public education on the problem was vital.

Friedman said human traffickers had traditionally targeted low-paid migrant workers such as labourers, but in recent years well-educated or well-off people had become victims.

“I think a lot of it has to do with Covid. When the bad guys and everyone else was forced to isolate, they came to realise that they could do criminal behaviour online,” he said.

Police warned the public over potentially fraudulent online job advertisements or messages.

A spokesman said that alarm bells should sound when people saw jobs that offered high salaries but did not require qualifications or experience.

The Security Bureau said it attached great importance to the incidents and urged the public to remain vigilant over possible recruitment scams. It said the Assistance to Hong Kong Residents Unit would follow up on cases concerning individuals who had not yet left the relevant countries.

The United States last month added Vietnam, Cambodia, Brunei and Macau to a human trafficking blacklist that already included Malaysia.

The US said the jurisdictions were singled out in the annual survey because of inadequate measures to stop forced sex work and a lack of help for migrant workers.

The US also left Hong Kong on its Tier 2 watch list for the third year in a row because it said the city’s implementation of trafficking victim identification procedures was “ineffective”.

The US also said the government had not enacted legislation to fully criminalise all forms of people trafficking.

The Hong Kong government has “vehemently objected” to the criticism of the city in the US report.