The barbaric incident took place near Balisahi village, about 170 km from Bhubaneswar on Thursday night.
A post-mortem examination conducted on the body recovered on Friday revealed that the girl was raped before being murdered, sub-divisional police officer R.C. Sethi told IANS.
Quoting her family members, police said the girl had gone to a nearby field with her father on Thursday and left for home alone. Her father returned home in the evening but did not find her.
Family members and other villagers searched for her and found her dead near a mango orchard with her hands and legs tied. Two heavy stones were placed on her body which also bore injury marks.
Villagers on Friday informed police who rushed to the site and sent the body for post-mortem examination.
"The preliminary investigation indicated that she was strangled after being raped by more than one person. We have not arrested any one so far. Investigation is still underway," the official said.