1. A system for generating a demographic profile for a set of at least one webpage, the system comprising: a computer processor; a webpage audience information gatherer operative for providing, for at least one webpage, training data including demographic information characterizing an audience of the webpage; and a predictor developing module using the computer processor to compute at least one content characteristic of said webpage and to develop a prediction process which if applied to said content characteristic would have predicted said training data, wherein the prediction process is constructed and operative to be employed by an audience predicting processor operative, for at least one new webpage whose audience is unknown, to compute at least one content characteristic of the new webpage and to generate predicted demographic information predicted to characterize said unknown audience of said new webpage by applying said prediction process to said new webpage's content characteristic, wherein said audience information gatherer is operative for: identifying user profiles with explicit demographic characteristics stated in a profile page; adding these user profiles to a user panel; and monitoring data stream in social media platforms of users in panel; identifying posts referencing at least one web page; and adding web page URI with demographic characteristics of user to a training data repository.