Brooke and Asinat, whose surnames have not been released, are both aged 13 and have been missing from Bury since 4pm yesterday (March 19).
Police said that it is possible that they are with a larger group of children.
They believe that they are using the travel network to get around the area and there have been possible sightings in Bury, Bolton, Stockport and Manchester city centre.
Asinat has brown hair and might be wearing a school uniform.
Brooke has blonde hair and might be wearing a cap.
Greater Manchester Police (GMP) have asked anyone with information about their whereabouts to contact police on 0161 856 2476 or 101.
A GMP spokesperson said: “Officers are becoming concerned about two teenage girls who have been missing for almost 24 hours.
“Brooke and Asinat, both aged 13, are believed to be using the travel network and there have been possible sightings in Bury, Bolton, Stockport and Manchester city centre.
“They were last heard from on Wednesday and it is possible the girls are with a larger group of children.
“Asinat has brown hair and is possibly wearing a school uniform; Brooke has blonde hair and is possibly wearing a cap.
“Anyone with information about their whereabouts should contact police on 0161 856 2476 or 101.
“Always dial 999 in an emergency.”
