Officers in Beijing said the investigation centred on online allegations that the star, 30, had “deceived young women multiple times into having sexual relations
They have made rapid gains in rural areas since it was announced almost all foreign troops would go by September.
The first accusation came early this month when a woman said he had assaulted her while she was drunk.
Mr Wu, one of China’s biggest celebrities, has denied all the allegations of assault.
The first to accuse him was 19-year-old student Du Meizhu, who posted on social media that she had met Mr Wu when she was 17.
She said she had been invited to a party at his home, where she was pressured to drink alcohol and woke up in his bed the next day.
Ms Du said seven other women had told her Mr Wu had seduced them with promises of jobs and other opportunities. She said some were minors.
At least 24 more women have since come forward alleging inappropriate behaviour.
Mr Wu has denied plying Ms Du with alcohol, and also rejected other allegations that he had enticed girls to have sex in return for benefits, raped girls while they were unconscious, and had sex with minors. Under Chinese law, under-18s are considered minors, while the age of sexual consent is 14.
“There was no ‘groupie sex’! There was no ‘underage’!’ he wrote on his social media account after the allegations were made.
“If there were this kind of thing, please everyone relax, I would put myself in jail!”