During the months of August and September, there were eight reported theft incidents.
The LAPD says the man targeted lockers at Equinox and LA Fitness centers in West Los Angeles, Van Nuys and Hollywood.
Authorities believe the same suspect is responsible for all of the incidents as well as two in Orange County.
Police say once the man steals from the lockers, he tries to use the credit cards at various stores in Los Angeles and Orange counties.
The suspect was described as a 35- to 40-year-old African-American male with a bald head. He wears glasses and stands between 5 feet 8 inches and 6 feet tall, and weighs between 215 and 230 pounds.
Anyone with information was asked to call authorities at (877) LAPD-24-7.