Police are hunting for a man who grabbed a teenage girl and attempted to drag her into parkland in a brazen attack in the city's north.

The 18-year-old was walking at Malcolm Creek Park in Craigieburn about 5.40pm on Thursday when she was set upon by a man wearing a black baseball cap and a white t-shirt.

He tried to drag the victim out of sight but she screamed, alerting a passer-by whose intervention caused the man to run away.

The man is described as Caucasian, aged in his 20s with a thin build and about 183 centimetres tall with dirty brown or dark blond hair.

The investigation is ongoing.

The Fawkner Sexual Offences and Child Abuse investigation Team are investigating have urged anyone with information to contact Crime Stoppers on 1800 333 000 or make a confidential report at www.crimestoppersvic.com.au

More to come.