Implementations generally relate to increasing engagement among users in a social network system. In some implementations, a method includes determining at least one social activity associated with an initiator user in a social network system. The method also includes enabling a token to be sent from an initiator device to one or more nearby devices, wherein the initiator device is associated with the initiator user, and wherein the one or more nearby devices are associated with one or more nearby users. The method also includes sending one or more invitations to one or more of the nearby users in association with the token. The method also includes performing one or more predetermined actions in association with the one or more nearby users based on one or more responses to the invitations.
DETECTING CO-PRESENCE IN THE PHYSICAL WORLD