An online system provides objects for presentation to a user via a virtual world, each object having an organic appearance for display. The online system receives sponsorship requests for sponsoring appearances of one or more objects in the virtual world. A sponsorship request includes information describing a sponsored appearance of an object and a bid amount identifying compensation to the online system for using the sponsored appearance. When presenting an object to a user via the virtual world, the online system selects an appearance for the object from the object's organic appearance and one or more sponsored appearances based on characteristics of the user and bid amounts in the sponsorship requests including the sponsored appearances. The online system then presents the object to a user via the virtual world using the selected appearance.