Officer Lopez of the Los Angeles Police Department tells PEOPLE that they do not suspect foul play and assume the death was from drowning; the LAPD awaits a toxicology report. Lopez added that the victim had been attending a small gathering of five or six people.
Moore, 52, was not home at the time, as she's traveling out of town. Police tell PEOPLE that her assistant was present when the body was found.
In a statement to PEOPLE, Moore expressed her shock over the death.
"I am in absolute shock," she said in the statement. "I was out of the country traveling to meet my daughters for a birthday celebration when I got this devastating news.
"The loss of a child is an unthinkable tragedy, and my heart goes out to this young man's family and friends," she continued. "I ask that you please respect the privacy of all concerned during this sensitive time."
Police have identified the deceased as Edenilson Steven Valle of Los Angeles, according to the Los Angeles Times.
Moore's daughter Scout Willis will celebrate her 24th birthday on Monday. Her younger sister, Tallulah Belle, 21, has been documenting their celebrations on social media throughout the weekend. The girls appear to be in New York City, where Scout has a home.
Eldest sister Rumer Willis was traveling with the Dancing with the Stars: Live! Perfect Ten Tour earlier this summer, but she was seen at LAX on Friday.
With reporting from JULIE JORDAN