Miles is 6-feet 2-inches and weighs 200 pounds.
Luluvioletta Mariposa Bandera-Magret is approximately 4 feet 5 inches tall and 75 pounds with curly brown hair.
They are 7-year-old Luluvioletta Bandera-Magret and 14-year-old Lilianais Griffith.
Round Rock police said they were called out to a home on the 2600 block of Leslie Court to conduct a welfare check. Griffith is 5-feet 10-inches, weighs 100 pounds, has brown eyes and has a right nose stud with braces.
Terry Allen Miles, 44, according to police, may have the children, but it's unclear what his relationship is to the girls.
Police are looking for Terry Allen Miles in connection with their abduction.
He is believed to be driving a gray, 2017 Hyundai Accent with a TX license plate: JGH9845. Miles has a beard, hazel eyes, and wears glasses. Police say their last possible sighting was northern New Mexico, southern Colorado.
He may be headed toward Louisiana, according to KHOU.
Law enforcement officials believe these children to be in grave or immediate danger.
Police are asking for help finding two Texas girls missing since Saturday, Dec. 30. The vehicle has a hatchback with a white sticker on the upper right-hand corner of the rear window. Anyone with any information is urged to contact Round Rock police at 512-218-5516.