What does Michael do, in Chapter 17, when he realizes Hanna has disappeared?

Michael first goes to Hanna's apartment at their usual meeting time. Michael realizes Hanna is nowhere to be found. Michael then calls the streetcar company and is informed that Hanna had not come in to work that day. Michael goes to speak to the owner of the apartment building, who tells him Hanna has moved out that very day. After that, Michael checks with the citizens' registration office, and he is told that Hanna has moved to Hamburg.