13. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: obtaining information associated with a mobile application of interest; determining a plurality of similar applications to the mobile application of interest along with a respective similarity score by querying a database of structured data; determining a plurality of keywords from the similar applications having a threshold level of statistical information relating to a performance of a respective keyword with each respective similar application; and extracting a new keyword for the mobile application of interest to use for identifying content items for presentation on the mobile application of interest by: calculating a projected statistical value for the new keyword using a weighted least regression of the statistical information relating to the performance of the plurality of keywords weighted with the respective similarity score of an associated similar application, and determining the projected statistical value for the new keyword exceeds a threshold value.
16. The system of claim 13 , wherein calculating the projected statistical value for the new keyword further comprises calculating coefficients for the weighted least regression using the statistical information for each application and the application of interest for each overlapping keyword.