Meanwhile, her boyfriend, fledgling Premier League footballer Andrew Hall, 19, is said to have been treated in hospital for a severed finger.
Peat died at the house party, held by a teenage boy, while his parents were on holiday.
Emergency services were rushed to the property shortly before 1:30am after receiving a report of someone being ‘fatally injured’, but were unable to revive her and she died at the scene.
Witnesses reported a teenage boy covered in blood leaving the half-term bash, held in Ampthill, Bedfordshire, early Saturday.
A police spokesman said: “We have begun a murder investigation after a woman died from serious injuries earlier.
“Officers attended the scene where a body was discovered and scenes of crime officers are now undertaking a full forensic examination of the area.
“A 19-year-old man has been arrested in connection with this incident.”
A spokesman for Stoke City FC said the club’s academy director understood he had been taken into hospital but said the circumstances were unclear.
He added: “The thoughts of everyone at the club are with Megan’s family at this time.”
Hall played this season for Stoke City’s under-18 side and scored the goal that put them through to the fourth round of the FA Youth Cup.
Friends and family, including Peat’s father David, have been to the semi-detached house in to lay flowers.
A note from David read: “Megan Moosay, miss you more than words can say. You will always be in my thoughts and forever in my heart. Love you forever, Dad.”
There were also dozens of messages left for the schoolgirl on the social networking site Facebook and Twitter.
Emm Giles wrote: “Meg, you’ll never be forgotten you made such a big impact on people and you made them happy, always knowing the right thing to say, your such a beautiful young lady pretty smiles, laughter when needed you were a role model to some i’ll never forget your attitude.”
Peat was a pupil at Harlington Upper School in Dunstable.