platforms dont produce passengers its the track that will do this. Some stations which come with track attached will nomaly have passengers, but a lot of what you want may be called invisible station/platform. These provide you with the track and passengers and you can place your own platforms. In both cases from the object tab select the ? and click on the track of the station, this will open a window that you name the station and the type etc. All passenger enabled track is found in the objects tab.