The 11 color screenprints were taken from businessman Richard Weisman's home sometime between Sept. 2 and 3, said Detective Mark Sommer of the Los Angeles Police Department's art theft detail.
Ten of the 40-inch-square portraits feature famous athletes of the 1970s, including golfer Jack Nicklaus, soccer star Pele and figure skater Dorothy Hamill. The other is of Weisman, likely a commissioned portrait.
A $1 million reward was being offered for information leading to the return of the artwork.
The original prints were on display in Weisman's dining room and his house was locked up. It wasn't clear exactly when the silk screen paintings were taken or how the thieves got into the home.
The theft was discovered by the family's longtime nanny who arrived at the home to find the large prints missing from the walls. She immediately went to a neighbor's to call police, Sommer said.
"This was a very clean crime," Sommer said. "(The home) wasn't ransacked."
It wasn't known exactly how much the prints were worth but Weisman tried to sell the collection in 2002 for $3 million.
Weisman's home contained other valuable artwork but the rest of his collection was untouched.
"The theft of Warhol's 'Athlete Series' represents a profoundly personal loss to me and my family," Weisman said in a statement. Weisman, who published a book about his art collection called, "From Picasso to Pop," declined to comment further, saying he did not want to interfere with the investigation.
A neighbor saw a maroon van in the driveway of Weisman's home around the time of the robbery, and police are seeking more information about that, Sommer said.
Warhol became internationally famous in the 60s for his iconic image of a Campbell's soup can, his avant-garde films and his parties that mixed celebrities, artists, intellectuals and other beautiful people at his New York studio called "The Factory."
According to a catalog of Warhol's work, Weisman commissioned the artist in 1977 to create portraits of sports figures, including Chris Evert, Kareem Abdul Jabbar, Nicklaus, Pele, Hamill, and Ali, said Brenda Klippel, the director of Martin Lawrence Galleries in Los Angeles, which has a large collection of Warhols.
"Warhol was always a portraitist and fascinated with anyone of fame or fortune, anyone in the public eye," Klippel said. "He wanted all of his imagery to be instantly recognizable. If Weisman was in his circle and had the money, he could commission what he wanted."
Detective Don Hrycyk said the weeklong delay in announcing the theft was to allow detectives to confirm the reward and gather descriptions and photographs of the missing artworks.