Police discovered the body of Katrina Monk in an alley off Bradley Road, Enfield, north London. She was only yards from her home in Newbury Avenue, about four miles from the school. Her hands were bound.
Details about how she died were not released. A post-mortem examination was due to take place late yesterday.
Scotland Yard said the search for Katrina began after her family reported her missing at 8pm on Thursday. She had failed to return home from Enfield County School in the afternoon.
She should have left school at 3.15pm and taken two buses on the 45-minute journey home. She was said to have telephoned a schoolfriend from a call box at 6pm.
When found, she was still wearing her school uniform. Police said: 'There are no obvious signs that she was sexually assaulted but that will not be known until after the post mortem.'
A helicopter and dog handlers had joined the earlier search and officers had visited several of Katrina's friends.
Katrina was 5ft 2in tall, of heavy build with very long blond hair which she usually wore in a pony-tail. She was wearing a green tartan dress, white blouse and black bomber jacket. She was carrying a brightly coloured satchel.
She was the youngest child in her family and lived with her mother, her mother's boyfriend and her brother and sister. Police appealed to anyone who saw Katrina after she left school and before her body was found to call the incident room on 081 807 9332.