Sienna, aged 16, was last seen in Southampton on Saturday, 25 February. She said she was returning to her home address in Gosport but never arrived.
Sienna is described as: white, around 5ft, of slim build and with dark brown/black hair that is long but always worn in a ponytail. She was last seen wearing a cream North Face puffa jacket, blue jeans and black shoes.
If you think you have seen Sienna since she went missing, or think you might know where she is, please call police immediately on 101 quoting 44220079636.