In the clip, a gang of girls between 13 and 14 approaches their victim, who is sitting on a bench, take her bag away and begin slapping her.
The violence escalates as they drag the 13-year-old to the ground and kick her in the head.
She is seen bleeding from the nose as her persecutors continue their mocking chants.
After the video was shared on Facebook and other social media, people began making comments suggesting the perpetrators should be beaten up themselves.
Police in nearby Reutlingen said that the victim reported the attack immediately and that they were investigating the perpetrators for grievous bodily harm.
But they added that the calls for further violence being made online were adding to the victim's trauma and making the situation worse.
They asked internet users and the media not to spread the video any further to protect those involved after some media republished the entire recording.