1. A method comprising: by one or more computing devices, receiving a request from a first user for a content page; by one or more computing devices, determining a page identifier for the requested content page; by one or more computing devices, determining, based on the page identifier, one or more second users, wherein the one or more second users are identified in the requested content page; by one or more computing devices, determining a plurality of content items based on one or more of the second users, wherein each of the plurality content items is owned by a second user; by one or more computing devices, determining one or more user features of the first user; by one or more computing devices, determining for each of the content items one or more content features; by one or more computing devices, calculating for each of the content items an expected value of the content item with respect to the first user based on the user features of the first user and the content features of the content item; by one or more computing devices, ordering the content items by decreasing expected value; and by one or more computing devices, delivering to the first user, with the requested content page, one or more of the content items as recommendations to the first user based on the ordering of the content items.
6. The method of claim 1 , wherein the user features comprise one or more previous requests for one or more content pages received from the first user.