A $100,000 reward has been offered for information about missing teenagers Kay Docherty and Toni Cavanagh, who vanished from Warilla 30 years ago and are presumed to have been murdered.The girls were believed to have been on their way to a disco in Wollongong when they were last seen on July 27, 1979.Their families received separate letters posted from the Kings Cross area in Sydney one week later, in which the girls said they were staying with friends and would be home soon. But there the trail ends.NSW Police Minister Michael Daley today joined Kay's twin brother Kevin and their mother Jean Docherty to announce the reward and appeal for anyone with information to come forward."Their families have spent the last 30 years wondering what happened to their daughters, and they deserve closure," Mr Daley said."I hope that the lure of a cash reward may encourage those with information, who may have been reluctant to come forward at the time, to help police bring those responsible to justice."It may not seem like much but if anybody has any piece of information, however small, it could prove to be the vital link police need to find out what happened."On the night the girls disappeared, Kay, 16, told her parents she was staying at Toni's house, and Toni, 15, told her family she was going to the movies with Kay's aunt and uncle.It is believed the girls were on their way to a disco in Wollongong, but it is not known whether they arrived there."There have been no confirmed sightings of the girls since they were seen at the bus stop at dusk on the evening of Friday 27 July, although there was an unconfirmed sighting in Queensland in 1984," Mr Daley said."Strike Force Mundawari has been formed to investigate the pair's disappearance and detectives are interested in any information which will lead to the arrest and conviction of those responsible for Toni and Kay's disappearance and suspected murder."Detective Chief Inspector Michael McLean said detectives had recently travelled to south eastern Queensland and interviewed witnesses in the Brisbane and Gold Coast areas."It has become apparent through inquiries that a high percentage of those who lived in the Illawarra and knew of the girls at the time they disappeared, have relocated to that area," Insp McLean said.Anyone with information has been urged contact Crime Stoppers on 1800 333 000.