While the use of virtual worlds for business collaboration has increased, there has been no systematic research to date that examines the effects of virtual worlds on socio-emotional communication, which is considered to influence team performance variables, such as consensus and group cohesion. To increase our understanding of the effects of virtual worlds, this study seeks to explore: 1) the effects of communication medium (Second Life versus instant messaging) and leadership style (transformational versus transactional) on supportive and critical communication, and 2) the effects of supportive and critical communication on cohesion, consensus, and group efficacy. Through two experiments of small, ad hoc groups performing a management decision-making task, we found an interaction effect between communication medium and leadership style on the expression of support. We also found that greater expression of support can lead to higher group cohesion, post-discussion consensus, and group efficacy whereas critical communication can lead to lower efficacy and group cohesion. We discuss implications of these results for both theory and practice.