Yes but:
1) If there is a registered forwarding address, you can get it from the Post Office by completing a request form and paying a nominal fee ($1 last time I looked).
1a) You can also mail to the former address and put “address correction requested” on the envelope. Again, there will be a nominal fee when it is returned to you.
1b) Whether you use either of these methods to serve, it helps to know where your defendant is currently residing.
2) Service can be made at the “usual place of business” pursuant to Code of Civil Procedure sect. 415.20(b).
2a) If you don’t effect personal service there, substituted service will have to be supported by a Declaration of Due Diligence and you will have to do a follow-up mailing after delivery to the Person In Charge. That will add 10 days to the time that service becomes effective. Given the normal timing for hearings in Small Claims, you probably should get moving.
2b) If terms like “Declaration of Due Diligence” and “substituted service” are just more “legalese” to you, use an attorney service to effect delivery and make sure that it’s done correctly. The costs of service are recoverable, if you prevail.