General Motors Co. plans to stop advertising with Facebook Inc. after deciding that paid ads on the site have little impact on consumers' car purchases, according to a GM official.

The move by GM, one of the largest advertisers in the U.S., puts a spotlight on an issue that many marketers have been raising: whether ads on Facebook help them sell more products. On Friday, Facebook is expected to sell shares in an initial public offering that could put a market value on the company of as much as $104 billion.

Executives have spent the last two weeks trying to convince investors that its advertising business makes it worthy of a sky-high valuation.

GM will continue to promote its products on Facebook, but without paying the social-media company, the GM official and other people familiar with the matter said. Many companies maintain free Facebook pages.

GM's decision raises questions about the ability of Facebook to sustain the 88% revenue growth achieved in 2011. Facebook said last month its first-quarter ad revenue was down 7.5% from the previous three months. Facebook blamed "seasonal trends" for the decline, as well as a greater number of users from outside the U.S., where ad rates are lower.