Social media platforms are created and exploited for various activities carried out individually or collaboratively and relying on different resources and tools. Social media platforms are inherently contextual; the context being defined as a specific activity carried out for a specific purpose with specific tools and resources, as well as with specific people. These contexts may be spread over different platforms. Thus, users need to collaborate across various platforms, they need to move their environments and data from one platform to another. Every task a person accomplishes has its own specifics. Hence, there is a strong need for users to be able to personalize (shape) their environments to suit their specific needs: by changing a set of tools, adding and removing resources, by adapting the graphical and functional parts of their platforms, and sharing resources with others. This thesis investigates the challenges of contextualization, portability and personalization within social media platforms through the following research questions. How can we model a user context in a social media platform? How can we enable portability: i.e., to access the same user’s environment from different social media platforms and to migrate an environment from one platform to another? How can we enable the easy personalization of user’s contexts? In the first part of the thesis, we formally define the space concept, that materializes the user’s context and represents an environment constructed by the user. We propose an OpenSocial space extension that introduces the space concept into OpenSocial specification in the form of Space model and APIs. In addition, we propose a way to build contextual widgets capable of adapting to the user’s context. In the second part of the thesis, we propose the notion of collaborative portable space con- figuration relying on the space configuration language. We demonstrate how portability of spaces can be achieved with OpenSocial. This includes the classification of various migration methods and scenarios of space portability. In addition, we propose a concept of portable platform interfaces. In the third part of the thesis, we define plasticity as a measure of a platform ability to be shaped according to users’ needs. To address plasticity, we propose the functional skin concept for personalization of graphical and functional interfaces. In addition, we propose cloud aggregation and sharing mechanisms.