lurker

In Internet culture, a lurker is typically a member of an online community who observes, but does not participate by posting or commenting. The exact definition depends on context. Lurkers make up a large proportion of all users in online communities. Lurking allows users to learn the conventions of an online community before they participate, improving their socialization when they eventually "de-lurk". However, a lack of social contact while lurking sometimes causes loneliness or apathy among lurkers.