In California, a company needs a "repossession agency" license to locate or recover a vehicle. The licensing is provided by the Bureau of Security and Investigative Services (BSIS), a division of the California Department of Consumer Affairs. Acting as a repossession agency without a license is a crime and grounds for a civil lawsuit in California.
You can verify whether a company is licensed as a repossession agency in California by searching the Department of Consumer Affair's licensing records. If you did not get the name of the company who repossessed your car, call your finance company or lender. If your finance company or lender will not give it to you, call the local police department, as repossessors must file a report of repossession within 24 hours of taking the car. If the company who repossessed your car is not a licensed repossession agency, the repossession should be reported to law enforcement and the BSIS, and you should contact a qualified attorney because you also may bring claims against the company and your finance company or lender.
Individual repossession agents do not need to be licensed, but they must be registered with the BSIS under a licensed repossession agency. You can verify whether an individual repossession agent is properly registered also by searching the Department of Consumer Affair's licensing records.