The online hangout Facebook said Tuesday it plans to let companies target their advertisements on the site based on what its users and their friends buy and do on the Internet. The initiative, which comes as Web sites look to boost advertising revenue by charging more for ads targeted to a user's hobbies, interests and behavior, could change the tone of the site and renew privacy complaints. In announcing the program, Facebook Chief Executive and founder Mark Zuckerberg said marketers must respond to the changing nature of communication, driven in part by social-networking sites like his. "Pushing your message out to people is no longer good enough," Zuckerberg told about 200 advertising-industry executives. "You have to get your message out to the conversations." The Facebook ad program follows by two weeks Facebook Inc.'s deal to sell a 1.6 percent stake to Microsoft Corp. for $240 million, spurning a competing offer from online search leader Google Inc. and valuing the Palo Alto, California-based Facebook at $15 billion, Zuckerberg made no mention of that deal in his speech Tuesday.