Investigators believe the body is that of Dane Chandler Williams, 23, who was last seen at Sixth and K streets about 2 a.m.
Homicide detectives went to the scene due to the "suspicious" nature of the fatality, according to authorities.
"There is nothing obvious to the naked eye that would explain why he died. At this time it is classified as a suspicious death," said Lt. Kevin Rooney, San Diego Police Dept.
Family members of Dane Williams say it was completely out of character for him to disappear. They say the Huntington Beach resident loved to surf and loved his job.
He went gone down to San Diego over the weekend for work. That's where police say Williams disappeared.
On Monday, friends and family members of Williams went down to San Diego to search for him themselves. They passed out flyers with Williams' photo on them, and posted them around the downtown area.
Authorities say Williams was attending the Action Sports Retailer Expo in San Diego. Williams worked at Hurley International, a sports apparel company.
Williams was last seen late Friday night. Friends say they were all hanging out at a restaurant at the Hard Rock Hotel in downtown. He left his friends at around 2 a.m. Saturday but never showed up at his hotel, which was located right down the street.
"We went from the House of Blues to the Hard Rock Hotel and that was the last I saw of Dane," said Jessica Bowland, a friend.
Jessica Bowland was out with Dane Friday night. She and her friends drove down to San Diego to meet Williams, but when they reached the Hard Rock Hotel they got separated.
"The friends that came down to San Diego, we had no idea that there was a downstairs bar," said Bowland. "So every time we contacted Dane in the place he said 'I'm at the bar, I'm at the bar.' And come to find out that there was two separate bars and that's probably why we never saw him after that."
Police say a homeless man claims he saw Williams near a downtown library Saturday.
CNS and Eyewitness News reporters Subha Ravindhran and Eileen Frere contributed to this report.