After posting widening losses, Amazon took a pounding on Wall Street Friday, raising doubts on whether investors will support chief executive Jeff Bezos' strategy of putting investment ahead of profit.

The shares tumbled 8.3 percent to close the week at $287.06, having slid some 28 percent from highs earlier this year.

Amazon said Thursday its loss in the last quarter widened to $437 million after a series of product launches including new phones, tablets and television programs.

The news from online retail giant, which is known keeping profit margins low as it grabs market share nonetheless stunned many investors and analysts.

"Frustration with Amazon is reaching peak levels," said Deutsche Bank analyst Ross Sandler. "We are struggling to identify a catalyst to break the negative momentum."

The loss in the third quarter was worse than anticipated, and far worse than the $41 million deficit in the same period a year earlier.

The loss came even as net sales increased 20 percent from a year ago to $20.58 billion in the quarter.

"We see further downside risk to the stock," said Barclays analyst Paul Vogel.

Vogel said Amazon's aggressive spending and soft growth outlook "may be too much for everyone but the most patient of investors."

- Facing Alibaba -

Shilpa Rosenberry, analyst at the research firm Daymon Worldwide, said Amazon is facing challenges at it tries to expand globally and goes up against new challengers like China's Ali Baba.

"While they're scaling fast internationally they're very challenged, especially as they're entering emerging markets where competitors like Alibaba have an advantage," Rosenberry said.

The US holiday season will test Amazon because "traditional brick-and-mortar retailers are stepping up," she said, warning that rivals like Target will offer free shipping without minimums.

Amazon this year has been moving aggressively in several areas, not just in traditional retail.

Bezos earlier this year announced the launch of its "Fire" smartphone, and later upgraded its line of Kindle tablet computers and introduced a streaming media player.

The company bolstered its online content with new original programs and ordered a second season of its dark comedy "Transparent," a move that boosts its challenge to video rivals such as Netflix.

The Seattle-based company bolstered its online gaming presence with a $970-million acquisition of the game platform Twitch, and expanded its "Amazon Fresh" grocery delivery service.

While some Amazon products and services have been popular, its smartphone market share has been "effectively zero," according to the Consumer Intelligence Research Partners consultancy.

Amazon took a charge of $170 million for inventory, mainly for unsold phones.

Yet some analysts say the company is on the right track with Amazon Prime, a subscription service which gives customers free shipping and access to music, videos and other online content.

- Being patient? -

"Amazon remains a very aggressive investor," said Mark Mahaney at RBC Capital Markets.

Mahaney added because of Amazon's marketing acumen and "excellent innovation track record" and suggested that its investments will pay off in the long run.

Amazon will reap benefits from the global expansion of its Kindle ecosystem, using tablets for content like books and films.

"We'll be patient," he said in a note to clients.

Tom Szkutak, Amazon's chief financial officer, defender the company's strategy in a call with analysts following the earnings release.

"We certainly have been in several years now of what I would call an investment mode, because of the opportunities that we've had in front of us," he said.

Szkutak offered no indication of a change in strategy, saying only "there's still lots of opportunity in front of us, but we know that we have to be very selective about which opportunities we pursue."

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