It took dozens of volunteers half a year searching old Chinese maps and villages, but finally the online-organised group helped Luo Gang find where he was kidnapped 23 years ago -- and his birth family.

The search for China's missing children -- mainly boys abducted by traffickers to feed a traditional hunger for sons exacerbated by the one-child policy -- is moving into cyberspace as desperate families turn to websites and social media.

Taken aged five from Sichuan province in the southwest to Fujian on the east coast in 1990, Luo shared detailed childhood memories with the website Baby Come Home and a far-flung crowdsourcing venture followed, culminating in a reunion.

"Luo Gang looked at the satellite map that (a volunteer) had circulated online... and soon discovered that an area near Yaojia village looked very similar to his home," said an account of the search on the site.

"Let us wish him a healthy and happy life going forward!"

Success stories such as Luo's remain the exception, but Chinese who say they receive little help from authorities see few other options.

"It's better than nothing, better than not having just a little help," says Hong Peiping, a 35-year-old factory worker in the southeastern province of Fujian, whose son went missing in 2009 at the age of six.

Like other parents, she says the police made little effort to find her son and instead "just took his physical description and what clothes he was wearing, and let us go find him ourselves".

Hong's brother gave her a computer to post details of her boy Yang Weixin online, arrange with other parents to look for their children together, and form an informal support group.

"A lot of online friends talk to us and comfort us," she said. "They encourage us not to give up, to keep living our lives and not to fall apart, so the child will still have a come to come home to."

Reliable estimates of the numbers of kidnapped children in China are difficult to come by, but the Xinhua state news agency said in December that since 2009 authorities had freed 54,000 minors and broken up 11,000 trafficking rings.

In its latest annual human rights review, the US State Department cited media reports as saying that as many as 20,000 Chinese children were kidnapped each year for illegal adoption, many within the country.

Domestic media have reported others being forced to beg on the streets or work as prostitutes.

In a separate review last year, Washington said China "does not fully comply with the minimum standards" to eliminate trafficking, nor did it "demonstrate evidence of increasing efforts".

Instead parents are using social media to harness the potential of China's online population, the largest in the world at more than 560 million.

The Internet remains heavily censored in China, but still enables people to more easily organise, share information and air their opinions.

One well-known website for finding children -- an account on the Twitter-like service Sina Weibo of Yu Jianrong, a scholar known for highlighting social problems -- has gained 220,000 followers since being set up two years ago.

More than 20,000 people have posted photos of red-cheeked babies and wide-eyed toddlers along with written descriptions on Baby Come Home -- though much of it is hopelessly outdated.

One family in the southwestern metropolis of Chongqing looking for their girl who went missing 23 years earlier offered glimpses of a child who no longer existed: "Short hair, big eyes, cross-eyed, a little chubby."

"She might not remember her family members' names, but she might remember her favourite sister's name Li Zhenggui. She might remember that her mum was a little deaf," they offered.

Grown children have also uploaded pictures of themselves in search of families they had left behind as infants -- including one man, Du Fusheng, who went missing at nine months old and now well into his 50s.

But for some children, such as Luo, the long years of hope paid off.

He searched his earliest memories and shared with Baby Come Home volunteers details such as a bridge, a river and a newly repaved road where he was kidnapped.

The group hunted down matching details from other sources, including lists of roads resurfaced around that time.

They scouted out potential villages and cross-referenced with those that had reported missing children, and after hitting several dead ends, finally found his family.

"Thanks to the volunteers who helped Luo Yang find his way home," said the account on Baby Come Home.

"And thanks to all those online friends whose names we don't know."