"We believe she's booked further travel in New Zealand in the upcoming days".
Detectives are investigating the disappearance of 22-year-old Grace Millane, who was last seen in Auckland on Saturday night.
Detective Inspector Scott Beard this afternoon said her disappearance was "out of character", after her family in the United Kingdom raised the alarm on Monday.
Grace Millane, 22, from Wickford, travelled to Auckland two weeks ago but alarms bells rang when she failed to respond to birthday well-wishes on Sunday.
Millane is said to have been in New Zealand for about two weeks, and was staying at a backpackers' hostel in Auckland city centre.
Detective Inspector Scott Beard said police had no evidence of foul play, but were keeping an open mind.
"The police investigation today has concentrated on her movements and activities in Auckland since she's arrived in New Zealand", Beard said.
"It's important that anyone who recognises Grace from this photo or saw her on Saturday night contacts Police immediately".
"We tried ringing up the hostel, which is the Base Backpackers in Auckland, which were very helpful trying to track her down", her brother said.
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Various sightings of Millane have her last wearing a black top, blue jeans and red sneakers. He said they were waiting for the British banks to update them on when Grace Millane's credit cards were last used.
"Last time we spoke to her she was in good spirits and was enjoying herself".
Grace's father David Millane, 60, is flying out to New Zealand to help with the search.
Her older brother said it was completely out of character for her not to be in contact with her family.
She has brown hair and brown eyes and is approximately 5ft 6in (168cm) in height, and 58 kg.
He said they had been in contact with the British High Commission in Wellington.
A spokesman for the Foreign Office said it is providing consular support to the family in the UK.
Base Backpackers were approached by Stuffon Wednesday but declined to comment.
Members of Grace's family have shared appeals for information on Facebook and more than 20 police are working on the case in Auckland.