Police in Uppsala were contacted in the morning by a woman who said she had seen a gang rape broadcast in a closed group on the site.
“You have been raped,” one of the men said at the end of the video and then laughed, according to the viewer.
Police later confirmed they, and “many” others, had seen the footage.
The Facebook group is said to have several thousand members.
Police confirmed that they had found three men, aged between 19 and 25, and one woman at a local apartment.
The men were arrested on the spot.
Josefine Lundgren, 21, called the police when she saw the video.