Che Labastide-Wellington, a college student from Kensal Green, was knifed in the heart at the 16th birthday celebration in Kenton, north London.
One of his 16-year-old friends, who cannot be named because of his age, was also stabbed multiple times.
The pair were attacked by a group of 17, several armed with knives, in a feud between neighbouring estates in north west London, a court heard.
Seven of the group are on trial for murder and wounding at the Old Bailey, central London.
Despite all the guests being searched before admission, one of the defendant's brothers took a machete with him in his rucksack, the court was told.
Prosecutor Crispin Aylett QC said that a flyer for the event was posted on Instagram, which meant that "inevitably a number of people who had not been invited got to hear about it".
He told the jury that a "small army" of youths descended on the gathering to "sort out" the victim, who was outside in the street.
Mr Aylett said: "Once the defendants' group had arrived... they immediately attacked as a group - surrounding Che and his friends.
"As Che and his friends tried to escape, the defendants' group - as a group - hunted them down."
Che, who was apparently carrying a blade himself, was knifed once in the chest and collapsed in a nearby alleyway on November 7 2015.
He was pronounced dead at the scene by 1.30am.
The second victim was chased down and stabbed six times in the back, side, arm and leg. He was taken to hospital and given six units of blood, which saved his life.
