Facebook Courts a Skeptical Madison Ave

General Motors, the third-largest advertiser in the country, shut down its Facebook budget, about $10 million, saying that those ads were simply not doing enough to sell automobiles. For Facebook, the loss of $10 million is not a big deal. The company generated $3.7 billion of revenue last year, 85 percent from advertising. But the loss underlines the company’s need to convince a skeptical Madison Avenue that Facebook pages are the perfect vehicle for marketers and to convince eager investors that it can increase its advertising revenue, and quickly. “It’s one of the most powerful branding mechanisms in the world, but it’s not an advertising mechanism,” said Martin Sorrell, chief executive of WPP, the giant advertising agency. G.M. aside, many companies remain committed to the social media platform as a way to engage and connect with consumers. Advertising executives, industry analysts and institutional investors just aren’t convinced that activity will translate into huge and growing profits for Facebook. It is a concern shared by some of the company’s bankers, according to people with knowledge of the matter.