1. A computer-implemented method comprising: storing, by an online system, a set of user profiles describing users of the online system, each user profile comprising one or more user attributes describing a user; receiving, by the online system, information identifying an input content item for sending to users of the online system; receiving a target audience criteria for selecting users for receiving the input content item, the target audience criteria mapping each of one or more user attributes to a set of values; identifying one or more content attributes describing the input content item; selecting a user attribute for determining a modified target audience criteria; determining a plurality of subsets of values of the selected user attribute, each subset of values associated with a set of users having a value from the subset of values for the selected user attribute; for each subset of users associated with a subset of values, determining a measure of interest of users of the subset of users in the input content item based on a match of user attributes of users of the subset with content attributes describing the input content item, wherein determining the measure of interest of users of the subset of users with the input content item comprises determining a value inversely related to the number of past interactions with a matching content item indicating a dislike towards the matching content item; selecting a subset of values based on the measure of interest of users of the subset of users associated with the subset of values; determining a modified target audience criteria based on the selected subset of values; and distributing the input content item to users selected based on the modified target audience criteria.