"Please get in touch with us and please, anyone who knows where she is get in touch with police," the family said.
Detective Constable Joseph Reuben, of Whangārei CIB, said police held serious concerns Simmonds, given the length of time she had been missing.
"Police are continuing to urge anyone who may have seen her or who has any information about her whereabouts to contact them immediately," Reuben said.
While police had been making a number of enquiries to help locate her since she was reported missing, they had failed to locate her.
Police believe she may have taken a taxi or may have been offered a ride back to her home on the day she went missing.
"Anyone who may have seen her that day, or who picked her up and took her anywhere, we need to speak to you," Reuben said.
He encouraged anyone who may have seen or spoken to Simmonds in the weeks prior, and since her disappearance to contact police.
"We also understand she may have had friends in the Auckland area, and she may have spoken to them about where she was heading that day, so we're asking them to get in contact too. We are doing everything we can to find her."
He said her family were extremely worried and wanted to make sure she was safe.
Simmonds was last seen wearing a dark coloured singlet and black jeans, and had three large black and grey backpacks with her.
She has a large distinctive tattoo on her upper left arm of a fairy tangled in vines holding an orb.
Anyone with information as to her whereabouts can contact Detective Constable Joseph Reuben on 09 945 4733 on or Crimestoppers anonymously on 0800 555 111.
