Officers are looking for Harriet Nimmo, 13, and Madison McKinder, 12, who were last seen together at Worthing railway station at 5pm on Friday (5 June).
PC Heather Burrage said: "We are concerned about Harriet and Madison due to their age and vulnerabilities. Please let us know if you see them or have any information about their whereabouts."
Police said Harriet is white, 5' 6", of medium build, has black hair work up and a beauty mole between her top lip and nostril. She was wearing a black coat, black trainers, black leggings and top.
Madison was described by police as white, 5' 7", of athletic build, with brown hair with blonde highlights which she sometimes wears in a bun and was last seen wearing black Puma leggings, pink Nike trainers and a white England rugby shirt.
Ring 999 if you see them, police said. If you have information about their whereabouts, report online or ring 101 quoting serial 1388 of 05/06.
The pair were found on Saturday (June 6), Sussex Police said.