Police said they are investigating whether the girls were raped at the party last week.
While they were at the party, a group of teens allegedly held the girls down, removed their clothes and sexually assaulted them, The Local.de said.
The girls escaped and went to a nearby apartment, where they banged on the door and asked for help, police said.
The residents of the apartment said the girls were shaking and crying, and one of them said they had been raped.
Eight teenagers, six boys and two other girls between the ages of 15 and 19, were arrested following the incident, police said, and three have since been released.