With the increased presence of digital imaging devices there also came an explosion in the amount of multimedia content available online. Users have transformed from passive consumers of media into content creators. Flickr.com is such an example of an online community, with over 2 billion photos (and more recently, videos as well), most of which are publicly available. The user interaction with the system also provides a plethora of metadata associated with this content, and in particular tags. One very important aspect in Flickr is the ability of users to organize in self-managed communities called groups. Although users and groups are conceptually different, in practice they can be represented in the same way: a bag-of-tags, which is amenable for probabilistic topic modeling. We present a topic-based approach to represent Flickr users and groups and demonstrate it with a web application, Topickr, that allows similarity based exploration of Flickr entities using their topic-based representation, learned in an unsupervised manner.