The share price dropped 10.5% to $459.84 (£290.56) in early trading, a day after Apple reported revenue figures that were below forecast by analysts.
Apple sold 47.8 million iPhones in the last quarter of 2012 and its revenues rose to $54.5bn (£34.4bn) - but the numbers fell short of its targets.
Earnings of $13.1bn (£8.2bn) remained flat compared to the year before, marking the first time tech giant had not boasted double-digit increases in earnings for several years.
Some analysts had expected iPhone sales to be around 50 million and revenues to be slightly higher and the company saw net profit at $13.1bn (£8.7bn).
The results are likely to rekindle questions over what Apple has in its product pipeline, and what it can do to attract new sales and maintain its rocket-like growth.
It was the third quarter that Apple has missed revenue expectations.
Competition from Samsung and signs that the smartphone market may be close to saturation have slowed Apple's growth.
Questions remain over the company's ability to innovate after the death of iconic co-founder Steve Jobs.
But chief executive Tim Cook said he was "thrilled" with the figures and insisted the company continued to focus on innovation.
"We're thrilled with record revenue of over $54bn and sales of over 75 million iOS devices in a single quarter," Mr Cook said.
"We're very confident in our product pipeline as we continue to focus on innovation and making the best products in the world."
Apple also sold 22.9 million iPads in the quarter, in line with expectations.
But only 4.1 million Mac laptop and desktop computers were snapped up compared to 5.2 million in the same period a year ago, while Apple shifted 12.7 million iPod portable media players this year in contrast to 15.4 million during last year's first quarter.