One put up a sign saying "Shame on those who poisoned our trees"; others left flowers.
Far North District Council staff went to door-to-door asking for information and checking whether anyone's home security cameras could have recorded the attack.
It is believed council staff were unable to identify the perpetrator and have now called in the police.
Sergeant Haydn Korach, of Kerikeri police, confirmed a formal complaint had been laid over the suspected poisoning.
A senior constable familiar with the area had been assigned to the case and would be working with the council and local residents in a bid to find out who was responsible.
He urged anyone with information to call Kerikeri police on (09) 407 9211 or Crimestoppers, anonymously, on 0800 555 111.
It is believed the council obtained some security camera footage which has been handed to the police. A police officer inspected the crime scene last Thursday.
If a suspect is found police could lay a charge of wilful damage.
The council could prosecute under the Reserves Act or even the Resource Management Act, which allows for fines of up to $300,000 for killing native trees on public land.