Hundreds of teenagers had to be dispersed from outside a home in Worthing, after a party invitation was reportedly shared on social media.
Police officers were called to reports of around 100 to 200 people causing anti-social behaviour outside a house in Poulters Lane on Friday night.
Locals said their cars were attacked in the street, while later in the evening an 18-year-old man was taken to hospital following an assault in South Street, Tarring.
Sussex Police are appealing for any witnesses to the assault to contact them.
The party is believed to have got out of control after details were shared publicly on Facebook, prompting hundreds of uninvited guests to show up.
Videos and photos shared on social media show hundreds of teenagers - who appear to be of secondary school age - hanging around outside the house after attempting to enter the party.
A spokesman for Sussex Police said:
"Police were called to reports of a group of around 100 to 200 people causing anti-social behaviour following a party at an address in Poulters Lane, Worthing at 8.30pm on Friday (23 February).
"Officers were quickly on scene and a Section 34 Dispersal Order was authorised, giving officers and designated police staff the power to disperse individuals behaving in an anti-social manner.
"The party was dispersed, and the area was cleared. Following the incident, police received a report of an 18-year-old man who was assaulted at around 10.30pm in South Street, Tarring. As a result of his injuries, he was taken to hospital and enquiries are ongoing to identify the suspect."
They asked anyone with any information about the assault to contact Sussex Police.
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