The 15-year-old girl was targeted as she walked home in south-east Birmingham.
She fell victim to the armed attacker at around 7pm on February 1 on Shenley Lane, Northfield.
She has been left “devastated” by the incident, which involved an unknown weapon.
The teenager has required surgery for a wound to her wrist, and received a minor injury to her head.
Police have appealed to members of the public for any footage caught on camera.
Det Chief Inspector Dave Sproson said: “This attack appears to have been totally unprovoked and has had a devastating effect on the young girl.
“We have spoken to her to get a description of her attacker and we have been trawling CCTV of the area to see if we have an image that could help our investigation.
“We understand attacks like this can be alarming to residents in the area, but we have had no further reports of suspicious behaviour and we have increased our patrols in an effort to reassure the public.
“If you have seen any suspicious behaviour within this area then I would encourage you to make contact with the police and report such incidents.”
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