Police have arrested a man in suspicion of murder and sexual activity or a missing child.
The body of 13-year-old Lucy McHugh’s was discovered in woodland by a member of the public at Southampton Sports Centre on Thursday morning.
The teenager was last seen at her home on Wednesday morning and she had been reported missing.
A post-mortem on Friday discovered she died from unexplained injuries.
Hampshire Police says the 24-year-old suspect remains in custody.
Detective Superintendent Paul Barton said: “This is a tragic incident and our thoughts go out to Lucy’s family and friends at this terrible time.
“We know Lucy left her house in Mansel Road East at 9.30am on Wednesday 25 July and did not return home that evening as expected.
“We’re really keen to know what she did after leaving her house and would ask that anyone who saw her, had contact with her or knows of her movements on Wednesday contacts the incident room.”
Lucy was last seen wearing a distinctive black jacket with white sleeves, with the logo for the band Falling In Reverse on the front and RADKE 01 in red on the back.