We suggest a Social Media Agency Robot that can be used for interactive communication between elderly people and the younger generation via existing Social Media. This robot system has been implemented on a cloud service and a single board computer embedded in a human-type robot, which is equipped with a microphone, camera, speaker, sensors, and network access function, so that elderly people can transmit and receive information by voice via Social Media without using smartphones. We employed LINE which is a proprietary application for instant communications on electronic devices such as smartphones. In LINE, we need to select a message destination address before sending messages. On the other hand, our developed robot is basically operated by voice due to realizing the simple user interface. Therefore, we suggested a message exchange learning-type destination estimation method that enables elderly people not to express a message destination address explicitly. We also designed the Social Media Agency Robot based on the service-oriented architecture that enables us easily to use open innovation such as external cloud-based services. We developed the prototype system including the message exchange learning-type destination estimation method. Then, we did an experiment to evaluate our prototype system at a house for the elderly with the care service and detached houses in the Nagasaki prefecture. We confirmed the effectiveness of the message destination estimation through the real message exchange experiment by the elderly. We also evaluated the usability of the prototype system through the interview with the experiment subject.