In order to obtain a divorce, you must file the Petition and Summons and also additional mandatory pleadings and serve these. This must be by personal service if the other spouse will not sign a Notice and Acknowledgment of Receipt of the pleadings, such as in the case as where the filing spouse does not know where the other spouse is. The normal procedure is to hire an investigator to find the other spouse for personal service, and you will normally need their date of birth and social security number.
In most cases, the investigator (make sure that they are licensed in California) can locate the other spouse. If not, then the investigator executes a declaration of due diligence and files it with a motion by the filing spouse for publication. This is expensive and can take several weeks or months to accomplish. If the judge orders service by publication (which is at their discretion), then the filing spouse can proceed by default once the proof of service by publication is filed with the court. An experienced attorney is needed for legal representation, since this is a very complex and complicated legal procedure and if the proper pleadings are not included in the publication order, then the publication may have to be repeated.
Roy Doppelt practices family law in San Diego with Pinkerton, Doppelt & Associates.