The girl, named Cleo, was last seen at around 12.30 pm in the Sandown area.
Officers say they are concerned for her welfare and are urging anyone who may have seen her to get in touch immediately.
She was wearing a white T-shirt, black elastic shorts, white socks, and black trainers.
She was also carrying a black, laptop-sized handbag with two handles.
Police believe Cleo is still on the Island and say she could have travelled to Newport.
Anyone who spots her is asked to dial 999 and quote incident number 1211.
UPDATED 6.45pm: The youngster has now been located, a Hampshire and IW Constabulary spokesperson said.