NEW YORK (CNNMoney.com) - It had to end some time.

Before Google, the iconic search engine, reported its fourth quarter results Tuesday, the company had crushed Wall Street's sales and earnings estimates in every quarter of its short history as a public firm. That streak is no more. And Google investors appear set to punish the stock on Wednesday. Shares plummeted about 12 percent in after-hours trading Tuesday.

So long $400? Shares of Google have been on fire since the company's IPO in 2004. But the stock looks set for a nasty tumble after missing earnings estimates for the first time.

Get ready for a dip. Google's market value could take a $15 billion hit after the company's latest earnings report.

Things change fast online--even for GOOG What Livedoor can tell us about where Google's stock price is going. (Read column)

Google reported fourth-quarter sales, excluding traffic acquisition costs (TAC), the revenue that Google shares with advertising partners, of $1.29 billion. That was in line with expectations. But John Aiken, an analyst with Majestic Research, an independent research firm, said earlier Tuesday that Google would probably need to report sales of $1.37 billion to impress Wall Street.

And more alarming to investors, the company posted earnings per share, excluding the effect of stock options costs and research and development-related charges, of $1.54 a share, well below analysts' consensus estimates of $1.76 a share.

However, during a conference call with analysts, Google chief financial officer George Reyes said that earnings took a hit largely due to a larger than expected tax rate that Google had to pay.

The company said its tax rate for the quarter was 41.8 percent, up from its expected level of 30 percent, due primarily to higher expenses allocated to international operations. Some analysts pointed out after the call that if Google's earnings were taxed at the 30 percent level, profits would have come in between $1.78 and $1.82 a share, ahead of consensus forecasts.

"Google and Google's management is viewed as being more mortal today then they were in prior days. I'm disappointed that there was no communication about the higher tax rate. That led to confusion," said Clay Moran, an analyst with Stanford Group.

Reyes added that Google's sales were hit by unfavorable currency comparisons. Revenue would have been better if not for a strengthening dollar, he said.

Still, shares of Google (Research), which rose 1.4 percent in regular trading on the Nasdaq Tuesday, plunged in after-hours trading following the release of the earnings and did not recover much during the conference call. Based on that drop after-hours, the stock could see its market value plummet by nearly $15 billion at the opening bell on Wednesday morning.

The stocks of several other Internet companies fell after-hours as well, including Google's top rival Yahoo! (Research), online auctioneer eBay (Research), Internet retailer Amazon.com (Research) and Net conglomerate IAC/InterActive (Research).

It's important to note that Google didn't necessarily have a bad quarter, however. Sales nearly doubled from a year ago while net income surged 82 percent as demand for online advertising, particularly sponsored-search marketing, remains extremely robust .

Chuck Richard, a vice president and lead analyst with Outsell, Inc., a research and advisory firm for the information industry, said that investors should not interpret Google's earnings miss to mean that the online advertising market is cooling. "The outlook for Google is still strong. The miss is not significant," Richard said.

Other analysts defended Google as well.

"The earnings shortfall was primarily due to a one-time adjustment to the tax rate," said Marianne Wolk, an analyst with Susquehanna Financial Group. "The results were generally in line with expectations but the market has become accustomed to Google doing substantially better than expectations so that's why you're seeing disappointment."

Moran added that the stock's drop was an overreaction. "In reality, the business trends remain strong. There's no change to the Google story," he said.

And Google chief executive officer Eric Schmidt expressed optimism about the company's results. During the conference call, he said that the company was very pleased with the company's results and noted that Google sees tremendous opportunity for growth going forward, particularly in international markets. Google said that revenues from outside the U.S. accounted for about 39 percent of total sales for all of 2005.

Schmidt also stressed that Google would continue to spend heavily on research and development in order to remain an innovative company. "We invest with a long-term view of the business. We are going to make some really big bets," he said.

The company has done a lot to broaden out its product line during the past few months. Google has recently unveiled a new video store where consumers can buy downloads of NBA basketball games as well as shows from the CBS network. Google also is testing a classified ads service called Google Base and recently announced an acquisition of a private company that will allow Google to place radio ads.

Google also announced a deal in December to acquire a 5 percent stake in Time Warner's AOL Internet unit for $1 billion. AOL is Google's largest affiliate customer. (Time Warner (Research) also owns CNNMoney.com.) During the conference call, Google co-founders Sergey Brin and Larry Page both stressed that Google will continue to roll out new features on a regular basis.

But since the stock is up more than 400 percent since the company went public in August 2004, Google clearly needed to beat the Street again to justify its lofty price. Based on Tuesday's closing price, Google traded at 50 times 2006 earnings estimates, a significant premium to the overall market. Several analysts had thought that Google was worth it because of the company's growth prospects.

Google's earnings miss is the latest in a string of bad news for the company.

The stock has fallen nearly 7.5 percent during the past two weeks due to concerns about how strong Google's numbers would be in the wake of similarly disappointing results from Yahoo! (Research), a couple of analyst downgrades to "sell" citing the stock's valuation and controversy surrounding the company's refusal to share search results with the U.S. government regarding a court case about legislation meant to protect children from online pornography as well as Google's decision to allow the Chinese government to censor search results on a Google site in China.

Some analysts have added that Google will soon face more significant competitive pressure from Yahoo! as well as Microsoft (Research). Microsoft's MSN Internet unit is set to launch a new online search tool for advertisers soon called adCenter this year. adCenter will allow advertisers to bid for keyword searches based on specific customer data such as age, gender and geographic location.

Analysts also asked Google during the conference call about why growth in Google's revenue from advertising partners grew at a slightly lower than expected rate. The company said that Google's sales from its own portfolio of Web sites increased by 24 percent from the third quarter while sales from Google's network of advertising affiliates increased by just 18 percent from the third quarter.

And since Google does not provide earnings guidance, it seems likely that analysts will now lower their first quarter and full-year 2006 forecasts. That could put further pressure on the stock. Analysts currently expect Google to report sales of $1.46 billion and earnings per share of $2 for the first quarter and revenue of $6.56 billion and a profit of $8.79 a share for all of 2006.

For a look at why some analysts still think Google is a buy, click here.

Investors boo Yahoo! For more, click here.

Analysts quoted in this story do not own shares of the companies mentioned and their firms have no investment banking relationships with the companies.

The reporter of this story owns shares of Time Warner through his company's 401(k) plan.