In its semi-annual survey of over 7,700 teens, Piper Jaffray found that 40 percent had an iPhone, up from 34 percent six months earlier and 23 percent a year ago.

"We believe it is a positive sign for the power of the iPhone among younger users that Apple was able to expand its market share with teens despite no new product launches between our spring and fall 2012 surveys," analyst Gene Munster wrote in a note to clients dated Tuesday.

"Apple appears well positioned to see continued growth in ownership with 62 percent of teens planning on purchasing an iPhone as their next phone. Android was the next closest smartphone at 22 percent."

The survey also showed 44 percent had a tablet computer -- of which 72 percent were iPads.

Among those who don't own a tablet, but plan to purchase one in the next six months, 74 percent said they would choose an iPad.

The survey results leave the firm "reaffirmed in our belief that Apple remains the pre-eminent technology brand for teens," Munster said.

Munster added that if Apple, as widely expected, introduces a smaller, less expensive version of its tablet, this "could eventually increase iPad ownership among younger users."

"Overall, we expect Apple devices to continue to expand in teen ownership and believe that the company is set up well to benefit from loyalty among its younger user base."

Apple shares, which have fallen from a peak last month above $700, rose 1.1 percent to $642.80 early Wednesday.

A survey by IHS iSuppli said the total PC market in 2012 is expected to contract by 1.2 percent to 348.7 million units, down from 352.8 million in 2011.

That would be the first drop since 2001, but sales have been sluggish for the past two years.

"There was great hope through the first half that 2012 would prove to be a rebound year for the PC market," said Craig Stice, an IHS analyst.

"Now three-quarters through the year, the usual boost from the back-to-school season appears to be a bust, and both AMD's and Intel's third-quarter outlooks appear to be flat to down."

IHS said a strong rebound could still occur in 2013, with more adoption of Windows 8 computers and newer, thinner notebook computers gaining tracking.

"Whether a newly configured PC space could then stand up to the powerful smartphone and tablet markets, however, remains to be seen," IHS said.

Analysts say PCs have taken a back seat to tablets and smartphones in recent months.

IHS said last month that global sales of tablet computers are expected to surge to 126.6 million in 2012, driven by the iPad and rivals.

Some analysts say tablet sales will overtake that of PCs by 2016, or possibly earlier.