Another question: As a privat pilot I can share the costs of the flight. But can I put an announcment on Craig's list to find someone who wants to come to California and split the bill and come as a passenger? Or do I need a commercial licence for that?
Not only would you need a commercial pilot certificate, you would need a Part 135 certificate. If the FAA caught you (even if you had your commercial certificate) they would most likely revoke all of your FAA pilot certificates.