Christopher Paul Neil, 32, who has taught in Thailand, South Korea and Vietnam, is also accused of having sex with at least a dozen Cambodian and Vietnamese boys, some as young as 6.
Neil is believed to be in Thailand, where police are trying to track him down through his network of friends. He flew here last week from South Korea, where he suddenly abandoned a teaching job. Cameras at the immigration counter captured his image as he arrived at Bangkok's international airport.
Thai police appeared to have few leads on exactly where Neil might be, though they had earlier expressed confidence that he would not escape their dragnet.
"He could be anywhere in Thailand. We have got calls from all over the place that they spotted someone who looks like him so we are dispatching policemen to find out more," police Maj. Gen. Wimol Powintara said at a news conference.
The officer said posters of the suspect had been prepared and hotels and tourism agencies were asked to help in the search.
"We appeal to the public and the media to help us look out for this man," he said.
Neil was identified by Thai police earlier this week after digitally scrambled images of him with victims were unscrambled and then released publicly by Interpol in an unprecedented international manhunt.
Three Thai youths who were 9, 13 and 14 at the time came forward Wednesday to tell police that Neil had allegedly paid them to perform oral sex on them in 2003, Wimol said earlier, adding that the Canadian also had sex with at least one other underage male.
The arrest warrant is based on the testimony of one of the boys, he said, describing how the victim said he was lured from an Internet cafe by a Thai man who took him to Neil's apartment in Bangkok.
Earlier, Wimol said the warrant was based on evidence from two boys but later corrected that to one.
The boys said the suspect showed them pornographic images on his computer at his apartment in Bangkok, and paid them each 500 baht to 1,000 baht for sexual relations (US$16; euro11 to $32; euro22), Wimol said.
The boys came forward to police after spotting Neil's photograph on television when his identity was revealed Tuesday by Thai authorities.
In Seoul, Choi Ki-hwan, an official at South Korea's National Police Agency, said Thursday that Neil first arrived in South Korea in 2000 and stayed for a total of four years and six months, based on records from the immigration office.
Police have not received any reports that Neil sexually molested children while in South Korea, Choi said.
The hunt for Neil began three years ago when German police discovered about 200 online photographs of a man sexually abusing children. His face was digitally obscured, but German police were able to reconstruct a recognizable image of the man who has eluded police for years, and Interpol circulated those images last week.
The suspect was identified with the help of hundreds of tips from people who responded to an unprecedented appeal by Interpol for public assistance.
More clues about the suspect's background emerged with the discovery of a page on the social networking Web site MySpace apparently created by Neil. Interpol officials said they believe the page was kept by Neil.
"Been kicking around Asia for the past five years, teaching mainly and finding other forms of mischief," read the profile, which also described him as "5 feet, 11 inches tall, slim and slender."
"I love teaching, can't get enough of it really," the entry says, going on to describe his passion for drama, musicals and karaoke.
Separately, friends have described Neil as outgoing and fun to be around. Co-workers at international schools gave mixed reviews of his teaching skills, but all described a man they believed to be harmless.
Before teaching in Asia, Neil had worked as a chaplain in Canada, counseling teens.
Canadian authorities have said they would seek his extradition. Canada has sex tourism laws allowing the prosecution for crimes committed abroad.