We use data on frequencies of bi-directional posts to define edges (or relationships) in two Facebookdatasets and a Twitter dataset and use these to create ego-centric social networks. We explore the internalstructure of these networks to determine whether they have the same kind of layered structure as hasbeen found in offline face-to-face networks (which have a distinctively scaled structure with successivelyinclusive layers at 5, 15, 50 and 150 alters). The two Facebook datasets are best described by a four-layerstructure and the Twitter dataset by a five-layer structure. The absolute sizes of these layers and themean frequencies of contact with alters within each layer match very closely the observed values fromoffline networks. In addition, all three datasets reveal the existence of an innermost network layer at ∼1.5alters. Our analyses thus confirm the existence of the layered structure of ego-centric social networkswith a very much larger sample (in total, >185,000 egos) than those previously used to describe them, aswell as identifying the existence of an additional network layer whose existence was only hypothesisedin offline social networks. In addition, our analyses indicate that online communities have very similarstructural characteristics to offline face-to-face networks.