"We know there are people out there with information that will help us finally solve this case.
"Relationships and loyalties change over time and our hope is that someone who has knowledge of Joanne's fate, whether they were connected at the time or told information later, will do what's best for Joanne and her family and come forward to police.
"We have not given up hope in this case, and we have been able to solve similar cases in the past where new information is brought to our attention decades later," says Vickers.
The reward will be paid for material information or evidence which leads to the identity and conviction of any person or persons responsible for any criminal offence committed against Joanne since she was last seen.
Vickers says immunity against prosecution will be considered for any accomplice who provides information or evidence to police, if they are not the main offender.
Payment may be apportioned if there is more than one claimant. The reward offer will remain in force until May 4, 2019.
Anyone with information is urged to contact their nearest police station.
Information can also be provided anonymously to Crimestoppers by calling 0800
555 111.