A pilot program to gather DNA samples from biological relatives linked to almost 800 long-term NSW missing persons cases is to be extended.
Police will next month establish collection points on the state's south coast with two pop-up centres already in use on the mid north coast since February.
The temporary facilities have so far captured saliva samples from more than 50 family members at Coffs Harbour and Port Macquarie.
The program follows a comprehensive review of operations by the force's Missing Persons Registry completed in 2019.
Since then, the MPR has re-examined all 769 long-term missing persons cases in NSW and identified a lack of direct or familial DNA profiles for a significant number of historical investigations.
Registry boss, Detective Inspector Glen Browne, says police are grateful so many people have so far come forward to be part of what can be a challenging process.
"Our efforts to further missing persons investigations are continuing," he said.
"We are once again calling on relatives of any missing person across the country, who reside on or near the south coast, to consider coming forward and providing a DNA sample."
DNA gathered during the program will be uploaded into what police call the Volunteer Limited Purpose Index.
From there, it will be searched against the registry's Unidentified Bodies Index.
"At the same time, interviews will be conducted with family members to capture further information that may assist investigators with ongoing inquiries," Insp Browne said.
Familial DNA samples are provided via buccal swab and only compared against missing persons databases in Australia.
The new south coast trial centres will operate in early May at Merimbula, Batemans Bay and South Nowra.