Service systems rely on internal interactions of service provider agents and the external interactions with customers in the design and delivery of services. Careful analysis and modeling of such interactions are essential to the design of effective service systems. This research focuses on service interaction networks in the context of the design and delivery of information technology (IT)-centric services. We develop and test a model of service interaction network effectiveness and investigate the effects of some of its structural properties on the effectiveness of service systems. We empirically analyze the validity of the model by using data from SourceForge.net and develop and test a set of specific hypotheses. The results indicate that network centrality and the network density have negative impacts whereas network size has positive influence on on service systems effectiveness