Miss Doyle went to the cinema with friends on Saturday night and was expected home in Southwick by 10pm.
She did not return, and her family last heard from her 24 hours later, when she called them to say she was in Croydon.
Police are concerned by her potential associations and are appealing for anyone who has seen her or know where she is to come forward.
A statement by Sussex Police said: “A 15-year-old girl has gone missing after leaving home in Southwick to go to the cinema with friends on Saturday evening.
“Jenny Doyle went out at 7pm and was expected home by 10pm, but did not return. She did contact her family on Sunday and said she was in Croydon and would be heading home. However, she has not been heard from since 9.45pm that day.
“She is white, 5’ 8”, of medium build, with shoulder-length red hair and a pale complexion. She speaks with an Irish accent. “She was wearing a cream coloured top, waistcoat, blue denim skirt, black leggings and either boots or trainers.
“There is concern for her because of who she may be associating with and police have asked for anyone who has seen her or who may know where she is to email [email protected] or call 101 quoting serial 1871 of 11/06.”
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