The case has prompted widespread outrage and vows by the federal government to combat crimes against women.
Brazilians reacted with shock after the May 21st assault came to light last week.
Graphic photos and videos of the unconscious, naked teenager were posted on Twitter, and several men joked online about the attack.
The authorities said the teenager had been raped in a shantytown on the west side of Rio de Janeiro as she was visiting her boyfriend, The Associated Press reported.
The girl told the police that she was briefly alone with him but remembered nothing until she woke up naked the next day in another building among dozens of men who had guns.
The first arrest came after the military police fanned out in search of four suspects who had been identified, the news organisation Agence France-Presse reported.
The police said they did not know if the boyfriend was one of the attackers.
The case has rocked Brazil, Latin America’s largest nation, and highlighted its deep-rooted problem of violence against women