Adidas is. Virgin is. Proctor and Gamble and Toys R Us are… are you? Using Facebook for advertising, that is.

A recent Business Week article reveals that advertising on this social network has quadrupled since 2009. Clearly that oft-repeated mantra, ‘go to where your customers are’ is having some effect in the marketing offices of these major companies. And with Facebook currently beating even Google as the site, we spend the most time on, that’s where you can be sure to find them.

All indications are that the Facebook user base is expanding. Need proof that even the silver surfers are embracing this 21st-century phenomenon with the best of them? Well, you might just find it in the fact that a certain 64-year-old is now getting to grips with wall posts and silly trivia quizzes. And even the recent Quit Facebook Day seems to have dented the ever-expanding userbase by very little indeed.

We’ve posted before about the ability to reach localized or highly specialized audiences through Facebook’s advertising network. While the big companies we mention above no doubt enjoy a massive budget and blanket coverage, you can do just as much with far less money. Like us to show you how? We’d be delighted.