Ms Whittington described her friend as just over five feet four inches (1.6 metres) tall, of slight to medium build with shoulder-length mousy blonde hair, green eyes and a cheeky smile.
"We are concerned about the state of Anna's physical and mental health," she added.
"We are desperate to get her the help she will need if she is still alive, and just want to get her back if something terrible has happened."
Police in Auckland were in charge of the file, but police throughout the Far North were aware that Ms Hynes had been reported missing.
Anyone with information is asked to contact police, either a local station or dial 111.