An online system customizes content items to be displayed on electronic displays. The electronic displays may be located at a venue with a large amount of foot traffic from users such as a park, airport, restaurant, shopping center, or airport. The system receives information from an electronic display describing users in vicinity of, or interacting with, the electronic display. For instance, the electronic display receives information from client devices of the users or by using sensors such as a camera that captures images of the users. Additionally, the system may receive interaction data generated by a touchscreen device of the electronic display. Based on the received information, the online system can select content items that are customized based on the interests of the users. The online system can also provide customized content items for display on a user's client device based on the user's interaction with an electronic display.