The perpetrators put up pictures and a video of the girl on Twitter, sparking a nationwide backlash. The incident occurred in a Rio de Janeiro slum over the weekend.
At a press conference Friday, police said they had identified four people who were involved, including one man who appeared in the video, the girl's boyfriend and two people who were heard on the video.
Police are investigating not only rape allegations but also possible violations of Brazil's Internet laws
The state-run Agencia Brasil news agency said Saturday a man who taken into custody for questioning. Seventy officers were involved in the search for suspects and drugs were seized, Agencia Brasil said.
"The extreme violence we're dealing (with) has shocked everyone. It even shocked the police," said Fernando Veloso, the head of the civil police in Rio de Janeiro.
Interim President Michel Temer condemned what happened and called for an emergency meeting of security chiefs from all of Brazil's states on Tuesday.
"It is absurd that still in the 21st century we have to live with barbaric crimes like this," Temer said.
The case has generated outrage.
In Sao Paulo, a mural with messages of solidarity to the victim was erected Friday.
Online, people reacted with memes and posts calling out to an end to Brazil's "machista" culture and demanding justice for the alleged victim.
'It was 30 against all of us!'
Police said the girl testified she went to her boyfriend's house Saturday and woke up in another house Sunday "with 33 men armed with rifles and guns."
Police said it was still unclear if there were "30 or 33 or 36" people involved.
They said the case was initially being investigated as a cybercrime when the video emerged at the beginning of the week and only later did the girl come forward.
A 38-second video of the girl, naked and unconscious, was circulated on social media.
In the video, two male voices are heard bragging about "more than 30" people having sexual intercourse with her. They show close-ups of her sexual organs and use vulgar language while poking at her.
One of the suspects also posted a selfie with the unconscious girl.
"Beyond the rape, the broadcasting of these images makes the life of the person eternally humiliating," Daniela Gusmao of the Brazilian Lawyers Association told Globo television.
Brazilians lashed out with anger on Twitter and Facebook, using the hashtags #estuprocoletivo or #gangrape and #estupronaotemjustificativa or "rape can't be justified."
On Facebook, users are posting slogans such as "we need to talk about the culture of rape" and "It wasn't 30 against 1, it was 30 against all of us!"
In one video on Facebook, a woman complains the media are ignoring the rape by "not one, not two, not 10 -- 30 men!"
In another video on YouTube, a series of women address the camera, with one saying, "Rape is a form of torture. It's one more form of torture," and it ends with the image of a girl crying and shaking her finger.
Others reacted in solidarity on Twitter, with @ClaraCryss writing, "being born a woman is living in the uncertainty if you are going to be the next victim of rape," and a user identified as nõviñhã noting, "Short clothes do not rape. Hours do not rape. Places do not rape. Drinks do not rape. Rapists rape."