BEIJING—The emotional meeting of a man in southern China and a young boy believed to be his missing son has drawn fresh attention to the country's problems with child abductions and to new efforts to use the Internet to find lost children.

Peng Gaofeng had been searching for his son Wenle since 2008, when the boy, then three years old, disappeared from a public square near Mr. Peng's small payphone shop. Earlier this month, his family got a tip from an Internet user saying he saw a boy resembling Wenle in photos posted online,...