Chloe Semple left her house on New Road, Shoreham at 6pm yesterday.
She had packed five bags of clothes but left her phone behind.
She was last seen by a friend in Goring at 8pm.
Chloe was last seen wearing a white crop top, black leggings and a green jacket with a hood and is described as five foot six with shoulder length brown hair with red dye in it.
Officers urge her to get in touch with family and police to let them know she is well.
Anyone who has seen her should call 101 or email [email protected] quoting serial 1253 of 07/11.