In what came as a disquieting surprise for most investors, Internet search giant Google Thursday reported weaker-than-projected results for the 2011 fourth quarter, largely due to lower advertising prices and the debt woes that hit Europe.

With Google posting a plunge in its fourth-quarter earnings - after having witnessed accelerating growth for four successive quarters -, the investors were disappointed because it had earlier been predicted that a robust online holiday shopping season in the US will allow the company to increase the prices for its advertisements.

However, with the average advertising prices during the quarter having dropped by 8 percent year-on-year, the text ads which are shown alongside Google's search-engine results, and are the company's key revenue-generator, suffered a big blow.

The clearly unsettling fourth-quarter results posted by Google - which undertook heavy expenditure to expand itself beyond its core search-advertising business - brought about a 9 percent plunge in the company's shares in after-hours trading on Thursday.

With Google having fetched less money per click on its omnipresent online advertisements, the executives of the company have opined that the decline in advertising prices was partly an upshot of the technical alterations made with the aim of delivering more ads which attract user's attraction.

About Google's slow fourth-quarter growth amid lower ad prices, Benchmark's analyst Clayton Moran said: "I think everyone underestimated how quickly the European online ad market would suffer" because of the debt woes that hurt the economy.