Walker, 39, has not been seen since August 14 last year, when she was captured on CCTV on Bassett St, Christchurch.
Police earlier confirmed they believe Walker was “the victim of foul play and is no longer alive”.
“Rowena’s partner at the time has so far declined to assist police with our inquiries,” said Carolan at the time.
“No person can be compelled to speak with police under any circumstances, and it is that person’s right to maintain his silence.
“However, as the last person known to have seen Rowena alive, his assistance is crucial to the investigation, and it is disappointing and frustrating that he is unwilling to assist us.
“I would strongly urge him to reconsider and do the right thing by Rowena and her family.”
Carolan said no digital footprint or verified sightings of Walker had been made since she was last seen.
“This absence of contact is deeply concerning for investigators and her family,” she said.
On Walker’s 40th birthday, Carolan said “what should be a time of celebration for her whānau is instead one of sadness and desperation”.
In April, police searched for Walker in the Christchurch red zone.
“The investigation team is working our way through a vast amount of digital information, and we continue to speak with witnesses and identify new inquiries,” said Carolan.
“There is still a lot of work to do, and the investigation team is dedicated and motivated to find Rowena.”
Carolan said anyone with information about Walker should contact police urgently.
“Report any information they think may be relevant, no matter how big or small,” she said.
“We are grateful for the information received so far, and we continue to ask the community to help us bring answers to Rowena’s family.”
Contact police online at 105.police.govt.nz, clicking “Update report”, or by calling 105.
Please use the reference number 251022/9026.
Information can also be provided anonymously through Crime Stoppers on 0800 555 111.