Police said they are concerned for missing teenager Amber Kolliari from Angmering.
Amber, 15, went missing with Chloe Postlethwaite on April 13 but Chloe has since returned home safe and well.
She is described 4ft 8in, of slight build and with very long brown hair. She was last seen wearing a black leather jacket, black top, black leggings and white Nike trainers.
Amber has links to the Brighton, Bournemouth, Gosport and Tower Hamlets area of London.
If you have any information please report online or call 101 quoting reference 1258 of 13/04.