Dongguan, China (CNN) When Han Yulai, a businessman in Dongguan, a town in southern China's manufacturing heartland, had clients in town for a factory visit or trade fairs, he would always offer them what he calls the "Dongguan standard."

In the evening, he'd take them to a KTV, a karaoke entertainment establishment often synonymous with sexual services.

There, a "mamasan" -- a name given to a woman in charge of running businesses at brothels -- would line up a dozen young women, mainly Chinese but also Japanese, Korean and -- the most expensive of all -- Russians.

"You choose one or two, sing and drink and have a bit of fun, and then go to a room upstairs for some 'business.' Not love, only business," said Han, who used a pseudonym as prostitution is illegal in China.

Today, doing that type of business is becoming increasingly difficult.

More than 2,000 hotels, saunas and massage parlors that catered to the city's migrant workers and visiting buyers were shut down , according to state media.

A hotel in a red light district of Dongguan, southern China

The raids lasted several months and their impact is still being felt more than a year later.

Empty red light districts

Indeed, at my hotel, a four-star establishment in the heart of Houjie, one of the red light districts, the massage and sauna floor still remain closed.

So are spas and KTV facilities at other hotels in the area that I visited.

On the streets, not one single "xiaojie" -- the Chinese word for miss that's also slang for prostitute -- is to be seen. In barbershops, often a front for sex services, staff seem to actually focus on customers' hair and nothing else.

Lin Jiang, a professor of public finance and taxation at Sun Yat-Sen University in Guangzhou, estimated that the raids could wipe out out 50 billion yuan ($8 billion) for businesses, including hotels, shops and restaurants. That's a tenth of Dongguan's city revenue in 2014.

He says it's impossible to know exactly what the financial losses were because officials have been too secretive.

"We can only estimate, we can't get the data to prove it."

Lin says the crackdown has caused financial pain in more ways than one. Dongguan's economy has traditionally relied on low-cost manufacturing. Efforts at growing high-end service industries and advanced manufacturing have been hampered by the high profile prostitution crackdown.

"The anti-vice campaign has hurt the city's image and this shadow won't completely disappear," he told

CNN.

Han, the businessman, agrees.

"We absolutely have fewer customers coming to Dongguan now than a year ago."

Going underground

But even if the go-go days of Dongguan's red light district are over, it doesn't mean the sex industry has disappeared. Rather, the trade has gone underground.

Han can no longer openly take customers to KTVs or saunas for the "Dongguan standard," but there are ways of flying under the radar, he said, like having your own contacts with go-betweens and "mamasans."

Getting contacts was far from difficult, as I experienced myself.

Coming back to my hotel one night, I was approached by the lobby boy. "You like massage?" he asked with a cheeky smile.

For 1,000 yuan ($160) I was offered 90 minutes in my room with "two beautiful Chinese girls." He gave me his number.

Right before the lift doors closed, he winked at me and made a risqué hand gesture suggesting a type of sexual service.

A hotel chauffeur also offered his services. As we were driving along a busy highway, he turned back to me and said "anmo, anmo?" -- massage in Chinese -- and made suggestive gestures with his fingers. I said I'd think about it and he gave me his business card.

In less than a day, I had two local pimps at hand should their services be required.

A pharmacy sells viagra in the southern Chinese city of Dongguan.

Social media 'hook-up'

Social media apps are also being used to connect supply and demand, especially China's mainstream instant messaging service WeChat. Since the women can't work at KTVs anymore, some of them instead linger around the building waiting for men to seek out their services.

By searching "People nearby" and selecting "Female only" you get a list of WeChat users in the area. Looking at their profile pictures, it doesn't take much imagination to figure out who's in business.

Chinese media reports that the sex trade is also believed to have shifted to one-on-one home service and phone appointments and on the streets during my visit, I didn't see any sex workers.

Greater risks

More than 250,000 sex workers were estimated to have worked in Dongguan before the government took action. Critics of the raids say the new underground environment has exposed sex workers to greater risks.

"Sex workers have always been abused by the clients and the police. After the crackdown the situation is the same. They are still subject to violence from these to groups," said Ann Lee, a spokesperson for Zi Teng , a Hong Kong-based sex workers' rights group.

Human Rights Watch said in a 2013 report that sex workers in China are subject to serious abuses, including police violence, arbitrary detention and coercive HIV testing. The police often fail to investigate crimes against sex workers by clients, it said.

Global Times, a newspaper under the Chinese Communist Party mouthpiece the People's Daily, quoted people as saying the crackdown is hurting an already disadvantaged group, and raised the possibility of decriminalizing the industry, "as sexual freedom is arguably a human right."

Lee hopes one day the sex trade could become "just one normal business activity" with healthier control and regulations.

"But in China, that's just a dream. It's still too controversial," she added.

Viagra

Most of the entertainment venues closed by police last year have been allowed to reopen and stricter rules took effect in April, according to Chinese media.

The new rules include : Banning massages in private rooms with locked doors or lights turned off; identifying overnight guests to local police; and banning employees from offering services away from massage parlors.

However, local pharmacies in red light districts continue to display ads for Viagra in their shop windows, with both original and ripoffs for sale.

A pharmacist laughed when asked if there's still demand for the potency pills after the crackdown. "Yes," he said, "Especially at night time."