Police were called to a fight in Pretoria St and King St last Friday and found a series of parties in the same Pretoria St flat complex.
Police said it appeared at least one of the parties was advertised on Facebook as an open invite. Police estimated the parties attracted between 100 and 150 people in their late teens to early 20s.
A number of people who attended the party have been interviewed, with a focus on any other partygoers who were injured in the brawl.
Rotorua police said they had seen many parties in the region quickly sprawl out onto the street, especially when they were advertised over social media.
Detective Sergeant Staunton said: "Enquiries to date have established that there is a strong culture amongst the late teens to early 20 year olds to attend themed parties advertised on Facebook."
"Some of these parties have got out of control with a mixture youth, alcohol and overcrowding leading to these parties spilling out onto the street where fights break out," said Detective Sergeant Staunton
Police are encouraging parents to find out where their teenagers are going and what their actual intentions are.