Sergeant Adrian Brogan said: “Helena, from Draperstown, was reported missing to us last Sunday, 24th November.
“She was last seen at around 11am in the area of the lay-by on the city end of the Foyle Bridge.
“It’s believed Helena had got out of her vehicle – a black Mitsubishi Outlander – at the lay-by and, at this time, she was wearing a long brown, possibly black dress.
“In a bid to trace Helena’s last movements, officers will be at the lay-by on the Foyle Bridge this morning where she was last seen and where her vehicle was located.
“Our officers will be distributing leaflets in a bid to jog people’s memories.
“The Mitsubishi will also be at the lay-by.“Helena is described as being 5′ 4” tall, with short dark hair and of a slim build.
“I want anyone who was in the area last Sunday, either driving or walking, around 11am to think back about who you remember seeing.
“Do you think you may have seen Helena, or saw her driving in the area? Perhaps you’ve captured what may have been her vehicle on your dashcam.
“If you have any information, no matter how small, please come and tell us either at our mobile station on the Foyle Bridge this morning, or by calling us on 101 and quoting reference number 771 of 24/11/19.”