Before the DM or chatroom, if you wanted to connect with a stranger pseudo-anonymously, you bought a personal ad. This week, we seek three films with classified ads as inciting incidents: “Desperately Seeking Susan” (1985), “Single White Female (1992) and the now 20-year-old “Ghost World” (2001). Romance, murder and vicarious living abound, plus the story of Chance and Noah answering an ad.