They arrested Dinh Van Phu 33, Nguyen Van Viet, 23, and Vo Quoc Thai, 28, on Saturday for "fraudulent appropriation of property."
The arrests came after police had previously uncovered a criminal network in which the Vietnamese collaborated with foreign criminals for human trafficking and online fraud.
It lured many people to a sex website where they had to pay money to view attractive women and buy their sexual services before duping them out of their money.
At the end of April, after a period of surveillance, police in Tay Ninh Province coordinated with the Svayrieng Province Military Command in Cambodia to dismantle the network and identify nearly 20 people involved in it.
They found that Phu and Viet connected with two Chinese men to create and run the network out of Bavet City in Svayrieng.
They established a company, rented premises to open an office and operated a website and sex app called "Lauxanh" targeted at Vietnamese men.
In September 2023 Phu "bought" 16 Vietnamese at US$500 per person from a network that lures them abroad with false promises of "easy, high-paying jobs."
He forced them to work 15 hours every day.
They were supervised by a Cambodian group, and anyone not meeting their daily scam targets would be punished in various ways.
Those who wanted to quit and return to Vietnam had to contact their families and pay a large ransom to the human trafficking group.
Their job was to post images of young and attractive women (without contact numbers) on the 'Lauxanh' sex app and use social media accounts to reach out Vietnamese men and ask them to download and install the app.
The app users had to register as club members to be able to view more images and directly contact the women without having to go through intermediaries.
Once the users registered for membership, Phu's group would ask them to pay membership fees and persuade them to transfer more money to "meet the women directly for buying sex."
Then they would feign technical errors, demand taxes, fines, verification money, identity fees, and more to milk the victims.
The group also used Telegram accounts to post images of attractive women offering "door-to-door" services.
The accounts would be in large group chats and their users would actively seek out those interested in buying sex.
The users would pretend to be women selling sex and send seductive images and promise devoted service.
Once a customer agreed, they would be told to transfer some money before meeting the women. But once they do so, they would be cut off.
Investigators estimate there are thousands of victims across Vietnam who paid over VND50 billion.
They are expanding the investigation, and urging victims to file complaints and cooperate with them.