A Philips Trust Air Rescue fixed wing plane has searched from Mokau to Port Waikato, including harbours and coastline, out to six nautical miles.
Coastguard air patrol have searched and continue to search the bays and harbours on both coasts of Northland. Coastguard units have also searched Hokianga and Houhora Harbours.
Maritime NZ is continuing to broadcast details of the catamaran on marine channels as it seeks sightings.
"Police are looking at a multitude of possible scenarios as part of this search, and this includes advising and liaising with Interpol, in the event that Mr Langdon has left New Zealand," police said this afternoon.
"If you believe you have seen Mr Langdon's vessel in the last few days, or you think you may have information which would assist the search effort, please contact your local police station."
Que's mother, Ariane Wyler, told the Herald this week that she separated from Langdon last year and has since been in a protracted custody battle.
Detective Sergeant Bill Crowe said this morning: "This is still very much a search and rescue matter at this time. We're liaising with Interpol and obviously communicating with other agencies that we believe may play a part in this."
Langdon's bank accounts and phone records are also being checked by police.
Police have been in contact with Wyler over the last two days, the Herald understands.
Wyler, who lives in Golden Bay in the South Island but is on holiday in her native Switzerland, said on Wednesday that she hadn't seen her daughter for 20 months.
"I am deeply distressed about this current situation and miss my daughter Que greatly. I am strongly convinced that they both are alive, well and safe.
"I sincerely hope that they are okay and oblivious to the fact that they are being searched for. I believe in Alan Langdon and his capabilities as a sea-going person.
"My gut feeling tells me that they are further offshore to the west."
Police have been searching shorelines north of Auckland and used a spotter plane to search the coastline.
Detective Senior Sergeant Stephen Ambler said police are conducting "local inquiries" which "centre on locating where they are now".
Wyler has since hired one of Australia's top child recovery experts, Col Chapman, to carry out his own investigation.
According to Fairfax, it is the second time Wyler has asked for Chapman's help.
"We hope to be in New Zealand within the next 48 hours to assist police and to offer resources," he told Fairfax.
"We are suggesting that by day 18 to 20, it becomes a case that something has happened - that they have left the area, so let's put a plane up in the air and search the area properly."
Que spent her first four-and-a-half years living on 14m catamaran Sanyasin with her parents, Wyler said.
In March last year the family was in Port Vila, Vanuatu when Cyclone Pam struck.
The category 5 severe tropical storm battered the island, claiming up to 16 lives and sinking at least 20 boats.
It sank Sanyasin and the Langdons were lucky to escape with their lives.
Langdon and Que lived at Mary Smith's home in Kawhia after returning from overseas at the end of July.
The family had used her home as a base for years in between travels.
Langdon, a stay-at-home dad, built the catamaran the pair left Kawhia in on Smith's front lawn. Smith raised the alarm on Boxing Day after Langdon and Que had been at sea without word for nine days. She described Langdon as a competent boatman who doted on his daughter.
"She was his best mate. He loved her to the max," Smith said.
