Police are calling out to the public for help locating a mother of four whose been missing for nearly a month.

36-year-old Shelley Crooks was last seen in Punakaiki, on the West Coast of the South Island on December 22.

Although there's been some reported sightings of Shelly, police say none of them are confirmed.

Sergeant Michel Bloom of the Greymouth Police said it's unusual for Ms Crooks to not contact her family - especially over the holiday period.

"Having just had the holiday period, and with no contact to the family- that's somewhat out of character for her."

Bloom said although she's an experienced tramper - they're still concerned.

"We are in direct contact with Ms Crooks family, who are naturally quite concerned about her wellbeing."

Michel Bloom said they'd like to hear from anyone who may've seen a woman hitchhiking - carrying a large blue or purple Kathmandu backpack - anytime from December 23, and anywhere between the lower North Island and Upper South Island.