Dinh Xuan Dai, 14, alongside Ha Dai Giang, Nguyen Hai Duong and Nguyen Quoc Duy, all 17, are under investigation for "rape of a person under 16," a crime punishable by between seven years in prison and death.
The four, who had all dropped out of school, are currently being put under home arrest, police said Monday.
Investigation found Giang first became acquainted with the 15-year-old girl via social media. On August 4, Giang invited her out after learning she had broken up with her boyfriend. The former later met with Duong, Dai and Duy to plan their assault.
The next day, Duy and Duong lured the girl to an apartment where, after intoxication, she was allegedly gang-raped.