Facebook reports that its quarterly profit nearly doubled as the world’s leading social network continued to add users, but investors baulked when the company hinted at heavy spending next year.

Facebook said it made $US802 million ($A867.73 million) in profit for shareholders on revenue of $US3.2 billion in the quarter that ended on September 30, while the number of monthly active users grew to 1.35 billion worldwide.

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“This has been a good quarter with strong results,” Facebook founder and chief Mark Zuckerberg said in a release on Tuesday.

“We continue to focus on serving our community well and continue to invest in connecting the world over the next decade.”

But news that the tech giant might be about to embark on a spending spree has reportedly spooked investors.

Facebook chief financial officer David Wehner said 2105 would be “a significant investment year” – an announcement that seemed to have an immediate effect on the market.

Facebook shares, which have been near record levels in recent days, dipped one per cent to $US79.99 in electronic trades after the news.

Facebook took in $US2.96 billion from advertising during the quarter, with approximately two-thirds of that revenue coming from marketing messages served up on mobile devices.

About 1.12 billion people on average connected with Facebook in September using smartphones or tablet computers in a 29 per cent increase from the same month a year earlier, according to the earnings report.