Informal learning plays a critical role in supporting instructional design (ID) students to develop knowledge and skills they will need as future employees and to establish their professional development trajectory. This survey study is part of a larger design-based study that seeks to design, develop, and evaluate a technology-mediated learning environment (TMLE) to integrate formal and informal learning activities in ID degree programs. The survey explored the usefulness and frequency of engaging in informal learning activities among ID students and alumni (N=26). The individual and environmental factors influencing the participant engagements in informal learning were also investigated. The survey results informed the development of design principles and a prototype to guide the creation of the TMLE. The survey results revealed that face-to-face communication and searching the Internet were the most useful and frequently used informal learning activities, respectively. Additionally, participants sought informal learning activities to support their PD trajectory and gain needed information.