Social technologies are transforming the Web to a place where users actively contribute to content production and opinion making. Social networking requirements are becoming a core part of the needs of modern enterprises too, which need ad-hoc Web platforms that incorporate the right set of social features for their business. This leads to the need to provide facilities and methods for developing such socially enabled applications. In this paper we propose a model-driven approach that is specifically focused on the development of Web applications that exploit social features. In particular, we describe an extension of the WebML notation (a Domain Specific Language designed to model Web applications), comprising a set of modeling concepts that encapsulate the logic of the interaction with the social platforms. Upon this, we define a set of design patterns that respond to the typical needs of enterprises and we show some sample application scenarios.