Facebook's long reach into the Web SAN FRANCISCO -- The social network Facebook filed papers Wednesday to become a public company and sell stock. It hopes to raise $5 billion. According to the SEC filing, Facebook earned a billion dollars last year - virtually all of it from advertising. The goal is to be a destination for all media, reports CBS News correspondent John Blackstone. To understand why Facebook has become so valuable to investors meet Emily Castor is from California, Walter Vatieri from Italy, and Tatjana Antin from Serbia -- friends because of Facebook. "It's a foundation basically for every kind of social interaction that we have on the Internet now," says Emily Castor. They were brought together by Zimride, an Internet site that organizes carpools -- but is available only to members of Facebook. "It was comforting to see that Jana had hundreds of friends on Facebook ... and she looked like she was friendly," said Castor. "We rented a car and just hit the road," said Tatjana Antin. Zimride's cofounder John Zimmer says, like many internet startups these days, his company is using Facebook as its front door . "When you log onto our service and we require Facebook and you log into 10 other services that require Facebook, it becomes this social layer for the entire Internet," said Zimmer. Which makes it really hard for people not to use Facebook. And that is Facebook's goal, to become the place on the Internet that people must use to connect with friends and businesses. Everything users do on Facebook adds to a detailed personal profile that Facebook then sells to busineses searching for just the right customer. While some worry about privacy, that hasn't stopped more than 800 million around the world from posting their profiles on Facebook. "It keeps me in touch with anybody, like I can find them online whenever I want because everybody's on Facebook all the time," said Tatjana Antin, the Serbian. Increasingly Facebook offers one place to do it all, from sharing photos to shopping. The social network doesn't want to be just a stopover on the Internet. It wants to be the destination users never leave. Full coverage of the Facebook IPO Facebook files to go public, plans to raise $5B Facebook S-1 form Facebook's IPO: more Yahoo than Google?