Lauryn Sizemore was last seen on March 30 inside the bedroom of her home in Dawson Springs, Kentucky.
Lauryn is believed to be with her stepgrandfather, Glenn Eugene Harper.
Harper is driving a maroon 2004 Hyundai Sonata with Kentucky temporary tag 9555994 and VIN: KMHWF25S24A935157.
A door on the back of the vehicle has a black piece missing.
Harper, whose brother and father live together in the Houston area, told a friend he is heading to Texas.
Lauryn is 4'8" and weighs 130 pounds. She has brown hair and hazel eyes.
Authorities say she was last seen wearing a gray hoodie with black strings.
If you see Lauryn, call 911 immediately.