Two people have been detained in the case and police are investigating if the girl was sexually assaulted before being killed.
A class 12 student, who had gone missing a few days ago in Lucknow, was found dead on Monday about half a kilometre from Chief Minister Akhilesh Yadav's residence.
The girl had left for school on February 10 but did not return after which her family filed a First Information Report at Jankipuram Police Station, police said.
The police tracked the girl's mobile phone to Barabanki and was found on a rickshaw driver. He said he had found the phone lying nearby which led the police to the girl's body.
Mr Yadav has directed DGP Javeed Ahmad to personally monitor the case and constitute a special task force.
Two people have been detained in the case and police are investigating if she was sexually assaulted before being killed.