The arrest came after police in Thailand detained a British man on suspicion of pedophile activities, and officers in Vancouver held a Canadian whose extradition to face a child sex charge - also in Thailand - had been sought.
Police in the Cambodian capital, Phnom Penh, raided the German suspect's hotel room Thursday and discovered him with the teenage girl, said Keo Thea, deputy chief of Cambodia's anti human-trafficking police. The German will face charges in court, Keo Thea said.
In Canada, Orville Frank Mader, 54, was arrested on arrival Thursday at Vancouver's international airport, said police Col. Apichart Suribunya, head of Thailand's liaison office for Interpol.
Thai police had issued an arrest warrant for Mader on Wednesday after an 8-year-old Thai boy said he was taken to Mader's hotel room by a Thai man in Thailand's beach resort town of Pattaya, said Apichart.
"We have asked Canadian authorities to extradite him because he has committed crimes in Thailand," Apichart said. Under Canadian law, its citizens can also be prosecuted at home for sex crimes committed abroad.
Mader's arrest follows the detention Tuesday of British man Paul Cornelius Jones, 39, following a raid on his Bangkok apartment where police said they found a computer containing photos of naked boys and girls. Jones, of Cardiff, Wales, has been charged with distributing pornographic photographs of children under age 15.
"What we are seeing is an increased level of awareness among the police structures (and) the establishment of specialized units that allow them to arrest the perpetrators," said Carmen Madrinan, executive director of End Child Prostitution, Child Pornography and Trafficking of Children for Sexual Purposes, a worldwide network of groups striving to end the sexual exploitation of children.
"Many NGOs (nongovernment organizations) are becoming more and more vigilant, keeping under observation and tipping off the authorities suspected child sex offenders," said Madrinan.
A French child rights group, Action Pour Les Enfants, said it had tipped off Phnom Penh police about the arrested German. But the Cambodia director of the NGO, Samleang Seila, said, "There are still many loopholes and gaps in the legislation system and the judiciary that enable perpetrators to avoid conviction."
The problem of Western pedophiles in Southeast Asia was highlighted by a worldwide appeal by Interpol that resulted in the arrest Oct. 19 of Christopher Paul Neil, another Canadian, who is accused of having abused Thai, Vietnamese and Cambodian boys.
The hunt for Neil began three years ago when about 200 photographs of a man sexually abusing children were discovered online. His face was digitally obscured, but German police were able to unscramble the photos, which were then circulated by Interpol. Public tip-offs helped police identify Neil as a suspect and he was arrested in rural Thailand.