"It's possible she may have become lost and sought shelter somewhere."
Michelle was last seen wearing a gold-coloured cardigan, a red floral medium-length dress and was possibly wearing a woven green/blue floppy hat. She was also carrying a patterned cream-coloured tote bag.
Teams were collecting and scouring security camera footage as part of the search.
"CCTV is one of the phases we are working on now either to see if Michelle has been picked up either in the Waitākere township or local train stations," police said.
As police completed the second night of searching, concerns were growing for the safety of Simpson, who was last seen walking along Wairere Rd around 11.30am Monday morning.
Over the past 48 hours, Police and Land SAR crews had conducted an extensive ground search of the area around where Simpson was last seen.
O'Brien said the main focus of the ground search had been on the surrounding streets – Wairere Rd, Caton Rd, Gregory Rd and Horseman Rd.
The search had been made more challenging with the rural location and police had been searching dense bush as part of the efforts, he said.
The Eagle helicopter had also conducted multiple aerial searches and unfortunately there had been no confirmed sightings.
"We are doing everything we can to find Michelle and return her safely to her family.
"We will continue to search the area by land and by air and today we have widened our search area.
"I know many local residents have been greatly concerned for Michelle and I want to thank everyone who has helped by checking their properties or spreading the word to help locate her.
"I also want to thank the volunteers from our local community who have gone around knocking on doors in the neighbourhood and doing leaflet drops."
Police had earlier urged residents in the neighbourhood to check their sheds, back yards or any area where someone may seek shelter.
They also asked residents in the vicinity of Wairere Rd, Caton Rd, Gregory Rd or Duffy Rd to check their security camera footage or dashcam footage if they were driving in the area between 11am to 2pm Monday.
Contact the Waitematā Crime Squad on 09 839 0697 if you think you might have spotted someone matching Simpson's description since Monday morning.
"Any information, no matter how small it may seem, is crucial to us at this stage so please contact us if you think you may have seen Michelle."
