BEIJING (NYTIMES) - The most shared post on Weibo, China's Twitter-like social media platform, is not a video of frolicking pandas or President Xi Jinping meeting world leaders, but a teenage boy's birthday message: "I'm 15 today. Thanks for being with me all these years."

Since that was posted in September 2014, it has been shared more than 335 million times, the most shared Weibo post ever, according to Guinness World Records.

The poster was Wang Junkai, leader of TFBoys, a wildly successful boy band in China. Since their debut in 2013, when the boys were just 12 and 13, they have won major Chinese music industry awards and amassed more than 20 million Weibo followers. Sales of band merchandise average more than US$17 million per month, according to Chinese news reports.

So what explains their appeal?

"I like them because they express such positive values," said Jia Su, a 24-year-old advertising worker in Beijing. She has followed the group since she was a university student and now manages the Weibo account of a fan club for TFBoys.

"They are nice, kind, hardworking. That's what the Japanese and Korean boy bands don't have."

Unlike many teenage pop stars in Japan, South Korea and elsewhere, the members of TFBoys display no signs of youthful rebellion. They decidedly do not walk on the wild side. They sing of studying hard and serving the nation. The group's music is cheerful with upbeat lyrics, and the boys' appearance tends toward neat outfits and sweet smiles.

The group is no accident, having been formed by a company, Time Fengjun Entertainment, using three boys - Wang Junkai, Wang Yuan (no relation) and Yiyang Qianxi - plucked from its trainee program.

The video for one of their most popular songs, "Manual of Youth," shows the boys dancing with comic book superheroes in a classroom aglow with pastel colours as they sing: "The sun of this world can only shine on me brightly because of confidence. The centre of this stage only flashes for me."

That wholesome schoolboy image has won TFBoys love not only from Chinese fans, but also from the government. They have twice been featured on the Chinese New Year television gala staged by CCTV, the state broadcaster.

The Communist Youth League's official Weibo account often promotes the group's activities. In April, it posted an item about Wang Yuan's receiving a special award from United Nations officials in China for his proposals on education.

On International Children's Day in 2015, the Communist Youth League released a video featuring TFBoys singing "We Are the Heirs of Communism," the song of the Young Pioneers, the Communist children's organisation.

In the video, they wear the Young Pioneers' signature red scarves and sing: "Love the country and the people. Fear neither hardship nor the enemy."

"One way the Chinese government controls the entertainment industry," said Zhu Dake, a cultural critic at Tongji University in Shanghai, "is by honouring and financially rewarding those who, from the government's perspective, are conveying positive values."

In this case, "positive values" means not just traditional values such as filial piety, social harmony and hard work, but also deference to the party line.

Chinese authorities are quick to discipline celebrities who break the rules, whether by indulging in illicit drugs, soliciting prostitutes or demonstrating sympathy for Hong Kong or Taiwanese "separatists."

Recent victims have included South Korean entertainers. Since South Korea agreed last year to allow the United States to install a missile defence system - called the Terminal High Altitude Area Defense, or Thaad - South Korean shows have been blocked from the Chinese Internet, and South Korean singers and actors have been barred from Chinese television.

"No company can risk sponsoring a 'bad boy' band that might end up on the government's blacklist," said Zou Dangrong, the chief executive of the Hunan Dangrong Film and Television Media Centre, which trains people to become online celebrities.

"The celebrities can't have a 'tainted history.' They can't just do whatever they want. That's common sense in China."

Zou said the TFBoys' success was also a sign of the progress of China's entertainment industry.

"Before the early 2000s, the mainland Chinese entertainment industry was dominated by Hong Kong, Taiwan, Japan and South Korea. Celebrities from those places were regarded as true stars," Zou said.

"But it's different now. We have the money, and the market. What's more, entertainment companies have learned the key to producing successful idols."

The TFBoys' fame is reaching beyond the music industry, and bringing film offers. Wang Junkai had a role in Zhang Yimou's movie "The Great Wall." Wang Yuan appeared in the film adaptation of the popular writer Guo Jingming's fantasy novel "L.O.R.D.: Legend of Ravaging Dynasties."

Jia said she was saving money for one of TFBoys' fourth-anniversary concerts in August. "I'm happy to do all this for them," she said.

"I love their persistence, their maturity, which is remarkable for people their age," she said.

"When I'm feeling bad, I tell myself, 'These boys are working so hard, so why can't I?'" How will she feel if, as these boys grow up, one of them breaks loose and does something really scandalous?

Jia did not seem ready to face that possibility. She paused before responding.

"Well, I don't believe they will," she said. "There's a Chinese saying: At the age of 3 you can already see what a man will be like when he is old."