Police say a missing 15-year-old girl could be in Milton Keynes or Aylesbury.
Jessica Peters was last seen in Northampton shortly before 8.30am and has not been seen since.
Her family and friends are becoming increasingly concerned for her welfare.
Jessica is 5ft 6ins and of slim build.
She has recently dyed her hair from blonde to brown and may be wearing a black and white hooded top.
Anyone with information is asked to contact Thames Valley Police on 101, quoting URN 282 of 5/8.