Methods, systems, and computer programs for triggering interaction with a Dynamic Online Community (DOC) are presented. In one embodiment, a method includes an operation for monitoring online activity of a user, which includes tracking user input on a web browser. The method further includes operations for detecting that the user is interested in a subject based on the online activity, and for determining whether there is a DOC topic that is associated with the subject. The DOC has members that have shown an interest in the DOC topic. In another operation, the method assigns the user to be a member of the DOC if the determination indicates that there is a DOC topic associated with the subject. The user is automatically recommended to join the DOC. DOC related information is provided to the user after the user is assigned to the DOC. In one embodiment, the online activity of the user is searching in a search provider's website.