Allowing students to ask questions in a university course is a crucial aspect of learning, which leads to increased learning effectiveness but also increased workload of the teaching staff. To reduce their workload, this paper presents the design of a chatbot for instantly answering students' questions on multiple common social platforms including Telegram, Facebook Messenger and Line. The chatbot can answer questions in natural language and commands. Once the teachers upload the necessary course-related information to an online database, the chatbot can answer questions on the course materials and course logistics (e.g., class schedule). The chatbot also supports a login system so as to provide answers according to different student profiles (e.g., schedule of their enrolled class and score dissemination). A survey on ten undergraduate computer science students showed that our chatbot can effectively act as an online tutor to reduce teachers' workload and will be a useful tool to be integrated into other e-learning platforms.