What can I do if the person has moved and I cannot serve them?

More self-filed claims die here than on any question of proof, and the sequencing mistake is what causes it. People file first and worry about delivery afterwards, then discover that a hearing date is approaching with nobody served and the fee already spent. California recognises personal delivery, substituted delivery at a home or workplace followed by a posted copy, and clerk-arranged certified mail that only works if the person signs for it. Each carries its own countdown measured backwards from the hearing, and substituted delivery needs the most breathing room because it does not take effect until ten days after the follow-up mailing goes out.

So locating them belongs at the front of the process. Lawful starting points include the address you already have, any employer you know of, a professional licence record, and a registered process server, who will frequently trace as part of the engagement for a modest fee. Where genuinely diligent attempts fail, a court can sometimes authorise another route, but that follows real effort rather than substituting for it. The reason to be thorough is what happens later: a judgment obtained without proper delivery can be challenged well after the fact, on a timeline measured in months, which means a shortcut here can undo the entire result.