Enterprise social networking (ESN) platforms have been implemented by organizations to support employees' collaboration. However, there has been a reported lack of user participation on these platforms. This study focuses on interventions that can be used to overcome barriers of usage. A case study was conducted at IBM to investigate the effect of several interventions to positively influence ESN acceptance within IBM's Human Resources (HR) function. In this study we combined two rounds of interview data with activity log data. We interviewed the initiators of interventions, and we interviewed the employees targeted by those interventions. The activity logs allowed us to contrast actual usage of the ESN by employees from HR vs. other organizational functions. Compared to other ESN studies this study explicitly identifies factors driving or inhibiting ESN use, and shows how these factors can be addressed by interventions to significantly increase ESN use. Our results can inform and enable other organizations interested in the design of interventions to increase the use of ESN.