Detectives were pictured scouring Darebin Creek in Heidelberg West on Monday morning.
It follows an anonymous call made to police last Thursday morning.
Police have urged that person to call them back in the hopes of securing more information.
“Investigators are urging that person to call back and provide further information or to make contact with detectives,” police said in a statement.
Zhang, 33, was last seen at her Epping home on February 1 wearing a pink nightgown and slippers.
A friend reported her missing the following day.