While Facebook earned $3.7 billion in revenue last year, mostly from ads, it will still have to prove to investors that it can grow those numbers. That will mean finding new ways to let advertisers access its base of 845 million users. Few companies rely so heavily on advertising, and the market has been skeptical of those models even though a Facebook ad can reach 65 million people on a typical day, more than twice the amount of people who saw ads on last year’s American Idol finale.