Sussex Police have told V2 Radion that they are urgently looking for information regarding missing 16-year-old Ahn Niht Vo.
The teenager was last seen near to the Chichester College campus in Westgate on Thursday evening (8 July).
He is believed to be wearing a red T-shirt with a black leather jacket, light blue jeans and white trainers.
Anyone who has seen Ahn or has any information about him is asked to ring 999 quoting serial 1685 of 08/07.