The teenager said seven other women contacted her to say Wu seduced them with promises of jobs and other opportunities.
She said some were under 18 but gave no indication whether they were younger than China's age of consent of 14.
Wu has been "criminally detained" on suspicion of rape "in response to relevant information reported on the internet" including that he "repeatedly lured young women to have sexual relations," the police statement said on Saturday. It gave no other details.
The pop star had previously denied the accusations.
"There was no 'groupie sex'! There was no 'underage'!" Wu wrote last month on his social media account.
"If there were this kind of thing, please everyone relax, I would put myself in jail!"
Source: ICHPL ImagineChina
The news was trending as the most searched topic on Weibo on Saturday night, and some users online started commenting on Wu's social media account, telling him to "Get out of China!"
Wu is a Canadian citizen, according to the police statement.
The official paper of the Communist Party, the People's Daily, weighed in on the case, saying in a short opinion post online that "Having a foreign nationality is not a protective talisman, and no matter how big the name is, there is no immunity."
The teenager publicised her accusations on social media and later in an interview with the internet portal NetEase.
A day after that interview appeared, at least 10 brands including Porsche and Louis Vuitton broke off endorsement and other deals with Wu.
If you or someone you know is impacted by sexual assault, call 1800RESPECT on 1800 737 732 or visit 1800RESPECT.org.au.