Facebook’s revenue may have hit new heights in Q4 but the social networking giant also saw a steep rise in expenses as it places bets on the future.

Fourth-quarter revenue grew by 49 per cent to $3.85 billion, driven by advertising on mobile phones and tablets.

Mobile advertising revenue represented 69 per cent of advertising revenue for Q4, up from approximately 53 per cent in the fourth quarter of 2013 — another sign of how the transition in online advertising from PC to mobile device is tipping money into Facebook’s coffers.

The next spurt of growth could come from video-based mobile advertising, according to analysts.

Mobile daily active users (DAUs) were 745 million on average for December 2014, an increase of 34 per cent year-over-year.

And mobile monthly active users (MAUs) were 1.19 billion as of December 31, 2014, an increase of 26 per cent year-over-year.

Interestingly, the company breaks out ARPU on a regional basis. The contrasts between regions are revealing. In Q4, ARPU for the US & Canada was $9 compared to $3.45 in Europe, $1.27 in Asia-Pacific and $0.94 in the Rest of the World.

However, 2015 will be a heavy year for expenditure, the company has warned, as it looks to build up prime assets including WhatsApp, Instagram and Oculus Rift.

There are already signs on the horizon, as costs and expenses for the fourth quarter of 2014 rose 87 per cent to $2.72 billion, a faster rate than revenue growth. The increase was thanks to higher spending in R&D (including salaries), as well as marketing and sales spending.

Net income in Q4 grew by 34 per cent to $701 million.

On a full-year basis, revenue increased in 2014 to $12.47 billion, a growth rate of 58 per cent. Annual net income was $2.94 billion, up from $1.5 billion.