Woman sought over Melbourne assault

Police are looking for a fifth person after a 20-year-old woman was allegedly assaulted, sat on and robbed at a Melbourne library.

Police allege a woman and four girls approached the victim about 9.20pm on Wednesday when one of the group punched her in the face, dragged her to the ground and sat on her while another of the group stole her phone.

A 13-year-old girl from Carrum Downs has been charged with affray, robbery and theft, while a 15-year-old girl from Carrum Downs has been interviewed and released pending summons.

Two other girls are yet to be interviewed and police have released an image of a woman as they continue their inquiries.