Collective cognitive responsibility (CCR) of individual members is important in knowledge creation communities. There are some possibilities to improve CCR through feedback functions that implement learning-support systems; however, it is not clear whether or not such function is effective in extracurricular activities. Our research target is "HighNyammer,"a bulletin board system (BBS) system for student-staff members who are working in "Classroom-M"as extracurricular activities. We developed "HighNyammer Social Scanner,"a tool comprising three types of feedback functions based on social network analysis to improve community members' CCR. To examine the effect of the function, we conducted two types of analysis: trends analysis based on HighNyammer logs and a questionnaire survey with student-staff members. A comparison between 2020 (with HighNyammer Social Scanner) and 2019 (without it) showed that HighNyammer Social Scanner helped student-staff members to perform as members with high CCR, especially novice members.