U.S. auto giant General Motors (GM) reportedly plans to halt its advertising presence on popular social media site Facebook, a move that the carmaker said was part of an ongoing review on its marketing approach and expenditures.

"It's not unusual for us to move our spending around various media outlets - especially with the growth of multiple social and digital media outlets," the American company said in a statement issued on Tuesday.

According to The Wall Street Journal, GM has set aside $US40 million for ensuring its visibility on the social networking site that is presently accessed by more than 800 million users worldwide.

However, only 25 per cent of the amount or roughly $US10 million was allocated to direct Facebook advertising and the rest for other social media advertising campaigns that include hiring media agencies.

The U.S.-based publication also said on its exclusive report that GM will maintain its Facebook page to advertise its products globally, a technique that many companies currently employ, which is understood to still be funded by the company's Facebook visibility budget.

"In terms of Facebook specifically, while we currently do not plan to continue with advertising, we remain committed to an aggressive content strategy through all of our products and brands, as it continues to be a very effective tool for engaging with our customers," GM said.

But an unidentified source cited by Reuters on its Wednesday report has suggested that GM was pulling out its Facebook ads because they were deemed ineffective in ramping up consumers' consciousness of General Motors car brands, which include the GM Holden models in Australia.

GM's latest move, according to Pivotal Research Group analyst Brian Wieser, underscored the "riskiness of the overall Facebook business model."

"It is not a sure thing. It sure looks likely that it will be one of the most important ad-supported media properties, but it's not certain because there will be marketers who are challenged to prove the effectiveness of the marketing vehicle," Mr Wieser told Reuters.

Also, other companies were starting to doubt Facebook's ability to actually deliver advertising results, The Journal wrote, which in their book would mean considerable spikes in sales figures.

Even as Facebook has been boasting off a global presence that attracts the attention of hundreds of millions, "companies in industries from consumer electronics to financial services tell us they're no longer sure Facebook is the best place to dedicate their social marketing budget," Forrester analyst Nate Elliott was quoted by The Journal as saying in a blog posting.

Yet for Jason Beckerman of Unified, a firm that specialises on social media marketing campaigns, GM's woes may have been mostly caused by misaligned Facebook advertising, an error that normally would lead to wasted advertising expenses.

"Without the proper planning and structure of your buys, you are asking for little to no results," Mr Beckerman told Reuters, adding that companies would naturally be dismayed by not-so-sterling advertising results without realising that their marketing pitches on social media sites must be accompanied by an appropriate approach.