The development of web 2.0 was powered by web services that are software systems designed to support interoperable machine-to-machine interaction over a network. It was the choice of standards enabling such interactions that favored communication among different systems and their mash ups. Facebook was the first social networking site to launch a service for developers that exposed its web services and the correlated APIs (application programming interfaces). This choice allowed programmers to create tools that could live within Facebook and turned the social networking site into a platform by enacting its programmability. In order to investigate the possibilities and the constraints offered by social media platforms, there seems to arise the necessity to integrate the analysis of frontend texts (such as posts or comments) and of social media communicative properties with the exploration of an underlying layer constituted by the network of relationships created within an application ecosystem and developed by using web services. The aim of the paper is to present a multi-layered approach to the study of social media platforms that combines the emerging subfield of Semiotic Technology with Platform Studies. The model is here applied to the analysis of Facebook Login Service.