Facebook has reported its fourth-quarter profits of $701 million, a 34% increase on the same period a year ago.

The company's advertising revenue grew 53% to $3.59 billion, with nearly 70% of that coming from mobile ad sales.

According to the social networking giant, it now has 1.39 billion active users each month, a 13% increase from a year ago.

In a statement accompanying the earnings, Facebook CEO, Mark Zuckerberg said: "We got a lot done in 2014."

Total profits for the year were $2.9 billion, almost double the total for 2013.

However, the amount of profit the company made on each dollar of revenue decreased from 44% to 29% from a year earlier, as the social network invested more heavily in marketing and research and development (R&D).

The amount Facebook is spending on R&D almost tripled to $1.1 billion this quarter, as the company spent considerable sums on developing its various acquisitions such as Instagram, WhatsApp and virtual-reality headset maker Oculus Rift, as well as its own in-house messaging products and video services.

Facebook also reiterated a common complaint amongst US firms this earnings season, saying its revenue would have increased by 53% instead of 49% if not for unfavourable foreign exchange rates.