12. The system of claim 11 , wherein the content item search engine uses the received search terms to search the index.
11. A system comprising: one or more processing devices configured to perform operations comprising: receiving, from the user device, a search query for a content item, the search query including one or more search terms; identifying a corpus of content items previously delivered to the user device by the content item management system, wherein the content items included in the corpus of content items are advertisements corresponding to content sponsors; creating an index of the corpus of content items previously delivered to the user device, wherein the index of the corpus of content items previously delivered to the user device is populated of a cookie stored at the user device; using the received search terms to search the index of the corpus of content items; determining that at least one content item in the index corresponds to the received search terms; and delivering, to the user device, a content item search result, the content item search result including the at least one content item corresponding to the received search terms.