A 14-year-old girl was grabbed by a "muscular" man in Canberra's south on Tuesday but managed to break free, hitting him across the face and fleeing, according to police.

The girl was walking along Heidelberg Street near the Vikings Club in Conder about 9am.

She was approached by the man, described as muscular and in his 20s.

The man spoke to the girl and allegedly grabbed her left arm.

Police say the girl then broke free, hit him in the face, and ran.

Authorities are now trying to find the man over the assault. He is described as Caucasian, with closely shaved hair and clean-shaven, wearing a black T-shirt and skinny jeans, with a strong Australian accent.

Anyone with information should contact Crime Stoppers on 1800 333 000 or via the website.