The 17-year hunt for her kidnapped son cost Ye Jinxiu her marriage, home and family. And when she found her boy, now a grown man and stranger, he wanted nothing to do with her.

Now 59, homeless and alone again, Ye roams the streets of Fuzhou on China's east coast helping other parents search for their children, devoting her failing health to what she knows is largely a lost cause.

Tens of thousands of children, most of them boys, are believed to be stolen each year in China. Most are sold within the country to meet demand fuelled by a one-child limit, traditional preference for sons, virtual immunity for families who buy them and, as parents like Ye complain, apathetic police.

"Having a child kidnapped is worse than having your heart torn out," she said, gazing at a huge canvas she had laid out by a bus stop, printed with "missing" adverts and chubby-cheeked faces.

"If someone rips your heart out it takes one second, you die and you're not aware anymore," she said.

"If your child is kidnapped and not found, then every day as soon as you wake up, your heart hurts from thinking."

China does not publish figures on how many children are seized per year but said it rescued 24,000 in the first 10 months of 2013, probably a fraction of total cases.

Many are stolen in the poorer interior and sold to families on the wealthier eastern seaboard, particularly provinces such as Fujian where Ye lives, said Deng Fei, a Beijing-based journalist who helps locate children.

Tens of thousands might be kidnapped every year and sold for tens of thousands of yuan each, he said, cautioning that estimates were rough. On a popular website dedicated to the cause 14,000 families have posted notices looking for lost ones.

Children in rural areas are especially vulnerable, as two in five live apart from their parents, who have migrated elsewhere for work and often left feeble grandparents in charge.

Police have sometimes refused to open cases because the low chance of cracking them might hurt their performance record, and they have resisted pursuing families who buy, Deng said.

Also feeding the trade is the sale of children -- sometimes by those most entrusted to protect them.

In December a doctor in northern Shaanxi went on trial for selling seven infants after convincing parents to give them up because of supposed serious illnesses, state media said.

Reports two months earlier said a couple in Shanghai sold their daughter to buy an iPhone. They claimed they wanted to give her a better life, with a wealthier family.

Yang Jing, a 35-year-old mother from southwestern Sichuan, told AFP she has spent 13 years trying to retrieve her son after he was sold to a richer couple in Jiangsu -- by her husband.

"They told me it didn't count as kidnapping... because the father gave him away," she said.

-- "I can't stop looking" --

Ye, in Fuzhou, said she criss-crossed more than 10 provinces after her then six-year-old boy disappeared in 1993, collecting rubbish, washing dishes and borrowing to pay her way, and sleeping in parks. She nearly died, she said, before her husband begged her to stop and finally left.

She claims she found the trafficker's home by 1995 but authorities only acted after years of pressure. In 2000 three men were sentenced to at most three years' jail and a decade later police found the son, Lu Jianning, she said.

The night before their reunion Ye could hardly sleep.

But her son did not even hug her. He stayed for a year while she took on more debt to pay for his schooling.

Then he disappeared, and he has not contacted her in two years.

"I don't regret looking for him. How he lives his life is up to him," Ye said. "When your child goes missing you can't stop looking."

She lays out her canvas in quiet places where police do not bother her and hands out fliers filled with youthful faces.

Two were brothers, "Dou Dou" and "Yuan Yuan", kidnapped as infants on the same day in 1991. A short-haired girl abducted on her way home from kindergarten in 2010 was described as "wearing a black-and-white cotton jacket when last seen".

Some passers-by paused to scan the descriptions. One, surnamed Zhen, blamed the government for failing to help the rural poor. "If they didn't have to move to the city, they could take care of their kids and there would be less kidnapping," he said.

Ye's struggle has cost her her health -- she coughs blood and can hardly see -- and she owes relatives "so much money that I'm afraid to go home", she says.

But, she said: "Just thinking about these cute kids breaks your heart.

"I found my kid but other parents haven't found theirs, and I can't stop looking."