He took her to the safety of a nearby bar where staff called police.
Her clothing was damp and she had received neck and facial injuries.
She was also shoeless.
Detective Sergeant Jason Crowe, who heads the investigation, praised the intervention of the man he described as "a good Samaritan".
"It was a hell of a thing to do."
The man did not want to speak about what had happened.
Officers carried out a scene search of the beach area where the initial assault took place and were now focused on tracking Taki-McLeod in relation to what had taken place.
He has several warrants for arrest for failing to appear in court and for domestic violence.
"This was a particularly nasty assault on a vulnerable victim and we are keen to find who is responsible," Mr Crowe said.
"We also want to speak to anyone who may have information about the attack and the people involved."
Mr Crowe said although the incident occurred in the early hours of the morning there were still people around the Marine Parade and foreshore area who may have seen something untoward or unusual.
"We urge them to contact us as soon as possible."
Mr Crowe said the young woman was in a safe place and being looked after.
Jason Taki-McLeod is described as a male Maori, 1.65m tall with short black hair and of solid build.
He may be in Hawke's Bay or Gisborne.
• Anyone with information about Taki-McLeod or any witnesses to the assault should contact Mr Crowe at Hawke's Bay Police on (06) 831 0700 or information can be left anonymously on Crimestoppers 0800 555 111.
