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.
Detective 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.”
West Midlands Pollice confirmed they had increased their presence in the area.
They assured locals they understood the nervousness they would feel following news of the attack.
They said there had been no other reported incidents of suspicious behaviour.
DCI Sproson added: “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.”
The man was described as white, with a large build and dressed in dark clothing.
He wore a dark hat and dark blue face mask, and a hooded sweatshirt.
The incident comes as police step up stop and search powers around Birmingham to tackle knife crime rates.
West Midlands Police said it was reacting to recent reports of stabbings and robberies.
The force added it was “looking to learn and improve” on the impacts on people in the city centre.
In the wake of a spate of knife-related incidents and stabbings in the West Midlands from 2019, mayor Andy Street expressed how “horrified” the area was with the surge of violent crime.
He said: “It is an awful situation and I send my sympathy to the families and friends of everyone affected.
“This situation is totally unacceptable and unprecedented in its seriousness.
“It must be tackled.
“I firmly believe an issue of this importance transcends the political divide and that everyone will want to play their part in working to protect our residents and young people in particular.
He added: “We must make it clear that we do not want to be a society where people feel it is acceptable to carry knives.”
The Chief Constable of the West Midlands Police announced last month he would step down from his position by the end of 2022.
He said: “It is a phenomenal police force and area to work in but you get to the stage where it is time for a fresh vision for the force.
“It is time to look for a successor.”
He added: “We are recruiting more officers, 20 percent of our force are students, and we are making more investments in tackling crime.
“For a long period of time we were shrinking, but now the force is growing, with around 900 more officers.
“That doesn’t replace all those we have lost but we are starting to see more capacity in the force.
“It is a time to be optimistic about resources coming to policing.”
His announcement came as statistics showed over 400 violent crimes are committed every day in the West Midlands.
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