Especially in the knowledge intensive service industry and times of virtual teams, there is a high need to support collaboration and information exchange between employees with IT. Whereas many organizations have recognized the great potential of Enterprise Social Networks (ESN) in this context, there is still a lack of well-founded and applicable approaches to make this potential visible i.e. to measure the success of ESN. To alleviate this drawback we propose a novel approach to measure ESN success covering the dimensions usage and business value. To illustrate the practical benefit and applicability of the novel approach, we provide an extensive real-world example from the service industry. In cooperation with a large financial services provider, the approach was successfully applied and led to an improved decision support for different stakeholder groups including system administrators and executive management.