SHANGHAI >> An online campaign to gather photos of Chinese kids begging on the streets is pressuring authorities to crack down on gangs that kidnap children for exploitation and is helping reunite them with families.

Many of the children seen begging in Chinese cities, often in the arms of women who may not be their mothers, are snatched from their real families by kidnappers and then sold into virtual slavery, forced to beg by gangs that sometimes maim them to elicit greater sympathy.

Several families have been reunited with their abducted offspring since Beijing-based social researcher Yu Jianrong launched a campaign last month urging people to post photos of such children on microblogs — websites similar to Twitter.

The effort is winning fresh support for efforts to protect children from such abuses, though some visitors to the microblogs have expressed worries over privacy issues and possible retaliation against kids by their abductors.

Yu would not comment directly when contacted Friday, saying only that he would not speak to foreign media before hanging up. In his blog comments, he has urged media to “cool” their coverage of his campaign — likely out of concern over official sensitivities.

Using children under the age of 14 for begging is illegal in China, but like many other outlawed practices is often tolerated, even in big showcase cities like Shanghai. Some, barely big enough to walk, stumble through subway trains, hands outstretched. Others sit out in the cold, on grimy sidewalks.

Children are sometimes forced to beg by their own relatives. But others are used by gangs that have kept alive a long tradition of trafficking in children, women and the disabled.

Yu began encouraging China’s increasingly active population of so-called “netizens” to post photos of children they saw begging after receiving a request from one follower of his microblog appealing for help with finding his missing son.

The sites on Chinese-language sina.com and qq.com have since posted more than 2,500 photos of children seen begging in cities across China. At least six missing children had been rescued as of Thursday, the state-run newspaper Shanghai Daily reported.

The campaign is part of a growing trend to use the Internet to help track down missing family members.

“Microblog miracle: Child Lost for Three Years Recovered,” said a headline in the usually staid Communist Party newspaper the People’s Daily. It showed a picture of Peng Gaofeng holding his 6-year-old son Wenle, who he recovered after Internet users spotted the child begging in a village far from the southern Chinese city where he was abducted.

Internet users had spotted the child after his picture was posted on another microblog last fall.

Wary of the potential, as in Tunisia and Egypt, for social media to be used as a tool for dissent, China generally blocks access to foreign sites like Facebook and Twitter. But domestic versions of such social media are thriving.

Such forums are a promising way to help address such social problems and a reminder of their potential for fostering positive changes, said Yu Hai, a sociologist at Shanghai’s prestigious Fudan University.

At the same time, “This is an alert that the government needs to do more for people,” Yu wrote. “I’m optimistic about this in the long run, but obviously there is a need for more official support.”

Earlier this week, authorities in Taihe, a district in neighboring Anhui province that is known to be home to some organized begging rings, issued a notice ordering people using disabled children for begging to turn themselves in within 10 days or face “harsh penalties,” according to a photographed notice posted online by the Shanghai newspaper Oriental Morning Post.

Reports said police in Taihe had so far rescued two disabled children and detained five suspects. “Using disabled children to beg is a criminal act,” warned a red banner across a rural road in Taihe, in a photo carried by the newspaper.

Chinese police have set up a DNA and photo database as part of a crackdown on human trafficking that began in the spring of 2009. As of September, 813 children had been returned to their families.

But the problem remains widespread. According to humantrafficking.org, a website set up to monitor the global situation, estimates of the number of children traded or sold each year in China range from 10,000 to 20,000. Often, kidnappers grab boys to be sold to childless couples. In other cases, girls or women are taken to be sold as brides or are tricked or forced into working in the sex industry.

“While the public applaud the far reach of the Internet, the effectiveness of the police and the repeated crackdown campaigns against human trafficking are being questioned,” noted a commentary Friday in the newspaper Global Times.