A data representation of auctions in an online auction system and a bidding history associated with the auctions and the online auction system are maintained in a computer system for multiple users. A set of the users to whom to promote a selected auction is determined based at least in part on the bidding history. A message that promotes the selected auction is sent to each respective one of the set of the users. The message includes a control configured to open a web page that facilitates bidding in the selected auction through the online auction system.