Systems and methods are provided for discovering advertisements on publisher web pages and for identifying placement pathways by which discovered advertisements have been placed on the publisher web pages. An advertisement tracking and discovery system may use multiple web crawler applications to explore multiple publisher websites. The web crawler applications may gather advertisement data that includes times associated with each request made by the web crawler application. The system may use the gathered advertisement data and the times associated with each request to determine the placement pathways by which discovered advertisements have been placed. Each placement pathway may include one or more advertising channels or combinations of advertising channels. The system may accumulate and aggregate advertising data associated with the advertisements and the placement pathways and display the aggregated advertising data to a customer.