The victim was described by the witness as a young Pakeha woman with long, blond hair, and was wearing a white top.
Police would like to speak to the victim, or anyone else who may have witnessed the incident.
Constable Briar Engel of the Waitakere Combined Investigation Unit says this is a relatively unusual situation where police have charged an alleged offender but are still seeking the victim.
"Although a charge has been laid it would still be of assistance to police as part of the process that we speak to the victim. It would also allow us to offer any necessary support to her."
Anyone with information can contact Constable Engel at Waitakere Police on 09 839 0600 Ext 97022, or anonymously Crimestoppers on 0800 555 111.