The 16-year-old received stitches at Edinburgh Royal Infirmary after he was allegedly stabbed in the neck with a broken bottle on Saturday night.
It is understood a teenage girl had posted about the party on social networking site Facebook while her parents were out – prompting up to 60 youngsters from across the Capital to descend on her Moredunvale View home.
Police today said they were coming up against a “wall of silence” from the youngsters who had been at the party.
Neighbours said the assault happened just half an hour after dozens of teenagers arrived at the two-storey house. They reported “fighting in the street” before the attack, which is thought to have taken place on a footpath running through the cul-de-sac.
Police rushed to the scene to investigate the incident, but are so far struggling to firm up evidence from young witnesses.
Detective Constable John McShane said the party-goers have been giving conflicting accounts of the evening. Although some are local, others had travelled from areas including Gorgie.
DC McShane said: “I believe it was advertised on Facebook and heavily attended by youths from 15 to 19 years old.
“The party was well-attended and it spiralled out of control. We are hitting a wall of silence; they are not speaking about the incident. Some are telling us that it happened in the garden outside while some are saying it happened inside.”
He said most of the teenagers had been “heavily intoxicated”, adding: “There has been some sort of weapon used to cause the injuries – potentially a smashed bottle. There was noise in the street at the time, and we will hope this will jog people’s memories who may have information that can assist.”
The father of the girl who organised the party, who declined to be named, said his thoughts were with the victim of the assault and that his daughter was in a great deal of trouble.
A neighbour, who asked not to be named, added: “The party had only been going on for half an hour. The girl had only invited about ten people round but there were more than 50.”
Witnesses are being urged to come forward with information by contacting Police Scotland on 101.