Just after midnight authorities were called to a party in a commercial business complex on Tinker Road in unincorporated Rocklin for a shooting.
When deputies arrived they say the scene was chaotic and many people were fleeing for safety.
Elk Grove resident Roderick Donell Totton, 18, was found outside the party suffering from a gunshot wound. Totton was transferred to Sutter Roseville Medical Center where he later died.
Authorities say the party was heavily promoted on social media.
During the day, a gym called Free Flow Academy is held in the Tinker Road complex. The gym staff did confirm that they had a party there, but they would not elaborate.
Detectives are asking anyone with information to call them at 530-889-7844.