Malila Howell has lived in anguished limbo for more than two decades after her teenage daughter went out to deliver birthday invitations and never returned.

“There’s this hole in my being-ness where she should be and she isn’t, because I don’t know what happened,” Ms Howell said on Monday.

“I don’t know where she is.”

Eighteen-year-old Rose Howell was last seen about 6.15pm April 11, 2003, walking along Perrys Road, Repton, in the direction of her home in Bundagen – about 25 kilometres south of Coffs Harbour on the NSW north coast.

Nine days shy of her 19th birthday, Rose had been to the Bellingen library to make party invitations to deliver to her friends, Ms Howell said.

It was not unusual for her to spend the night at a friends’ home.

Her mother reported her missing on April 13, 2003, when she failed to return home for an appointment.

NSW police on Monday announced a $750,000 reward for information that sheds light on Rose’s fate.

Her heartbroken mother hopes the money will help jog the memory of someone who may have noticed something at the time she disappeared.

“Somebody, somewhere has got some idea of what would have happened to her and we’d really like to know,” she said.

“Her father died before knowing what happened to her … she’s got three brothers who don’t know what happened to her, various friends, aunties and other family members. ”

The grief of not knowing what happened had left Ms Howell “always a bit on edge, always anxious, always anguished”.

“It hurts still 20 years later,” she said.

She still dreams “that maybe she’s just gonna walk around the corner one day and reappear”.

“That’s a hope that I have deep inside, but it’s quite hard to accept that she might be dead or that she’s probably dead.

“While she’s not around, I don’t have to believe that until there’s some kind of proof.”

Rose is described as being of Caucasian appearance, with an olive complexion, about 160-165 centimetres tall, with hazel eyes.

Her mother remembers her as a quirky, funny person who played bass guitar and sported a Mohawk.

“People around knew who she was even if they didn’t know what her name was. She stood out. She was tall and stately,” she said.

Homicide detective Danny Doherty hoped that despite the passage of time, someone might come forward with information to help police crack the cold case.

“There’s people out there in the community who may have held on to a bit of information or a dark secret who may have information that could put that to light,” he said.

In 2012, a coronial inquest found that it was likely Rose had died. The date, place and cause of her death were undetermined.

-AAP