Social media applications such as wikis, blogs or social networks are being increasingly applied in firms. These applications can be used for external communication and internal knowledge management. Firms can potentially increase their productivity by optimising customer relationship management, marketing, market research and project management. On the other hand, the use of social media might lead to shirking among employees and might be, in general, very time-consuming preventing employees from managing their normal workload. This might lead to a decrease of labour productivity. This paper analyses the relationship between social media applications and labour productivity using firm-level data of 907 German manufacturing and service firms. The analysis is based on a Cobb-Douglas production function. The results reveal that social media might be related to labour productivity in an negative way which points towards a suboptimal use of social media.