There are two common terms:
platform — a major piece of software, as an operating system, an operating environment, or a database, under which various smaller application programs can be designed to run.
Within the scope of social media, a "platform" would be any piece of software that enables its users to engage in social media activities.
Service is also used to describe social media products that provide a set of services. These are referred to as "social media services" and would accurately describe the examples in your post.