Informal leaders can have similar effects on firm performance as formal leaders. Although informal leadership can play a critical role in organizational functioning, empirical research concerning this issue is scarce. I conceptualized informal leadership as a continuous variable, and tested the relationship between informal leadership and the following variables. First, this study examined how informal leaders can influence over other members, even though they do not possess formal power. Five indicators, i.e., performance, turnover intention, career satisfaction, work engagement, and optimism were selected to assess the qualities of informal leaders as role models. Second, this study advanced our understanding of how demographic factors (i.e., age, educational background, and work experience) contribute to shaping informal leadership. In addition, T-test was chosen to test whether informal leadership is more noteworthy in women than men. Lastly, this study compared the effects of informal and formal leaders on team effectiveness.