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Own Facebook? You'll want to know what this is. See No. 3 for more details Image source: Facebook

Social-media site Facebook (NASDAQ:FB) is firing on all cylinders. In the recently reported second quarter, the company reported a year-on-year top-line increase of 39% on the back of strong advertising revenue increases.

For investors, however, the important question is: Can Facebook continue to grow at this healthy clip? Specifically, what plans and strategies does Zuckerberg and Co. have in place to continue to grow its business? Here are three ways Facebook can continue to grow its top line.

No. 1: Growing its user base
Although user growth has slowed in Facebook's core business, it's still pretty solid on a comparative basis. For the recently reported second quarter, Facebook grew its monthly average users, or MAUs, by 13.1% over last year's corresponding quarter. Microblogging site Twitter grew its worldwide MAUs 15% on a year-on-year basis last quarter. However, when you compare Facebook's scale of nearly 1.5 billion MAUs to Twitter's 316 million, you can see that Facebook's growth is still enviable.

Perhaps the best way for Facebook to grow users from its current host of businesses is from its Instagram product. Recently, the company reported 400 million monthly active users, pushing past Twitter in the process. But perhaps the most-shocking thing was how quickly Facebook got to this figure -- in December, the company reported 300 million users, putting the annualized growth rate north of 40%.

That's not bad for a $1 billion investment, especially when the deal was considered overpriced at the time Facebook purchased the site in 2012. Facebook was considered foolish to pay so much for a company with no revenue; Instagram seems like a bargain now.

No. 2: Growing average revenue per user
The other way Facebook can continue to grow revenue is to grow average revenue per user, or ARPU. Unlike user growth, which has an outer bound at the earth's population in the long run and a short-run outer bound of only the 40% of the world that currently has Internet access, Facebook can continue to grow ARPU. And according to a research note from research firm eMarketer (via Re/code), Facebook will continue to grow its ad revenues on a per-user basis.

On a worldwide basis, eMarketer reports Facebook will book ad-based revenues of $12.76 per user in 2015, up 27% from 2014's figure of $10.03. According to the analytics firm, that figure will increase to $15.18 in 2016, and $17.50 in 2017, growth rates of 19% and 15%, respectively. In the United States, those figures are even larger: eMarketer thinks Facebook's ARPU for U.S. users will grow from $34.68 in 2014 to $73.29 in 2017, good for an annualized growth rate of 21%.

No. 3: Monetizing this new business
When it comes to new businesses, Facebook has an interesting opportunity in virtual reality. The company's purchase of Oculus VR is starting to bear signs of fruit. Recently, the company announced it would soon bring its virtual reality headset, Oculus VR, to market for the rather affordable cost of $99, a move that should spur adoption.

Perhaps the best news from the company is a host of content partnerships with Netflix, Hulu, Twitch, and Vimeo for content. The company's headset should be available in November. Look for a small contribution to its top line initially, but this could be a huge opportunity not priced into the company's valuation.

Jamal Carnette has no position in any stocks mentioned. The Motley Fool owns and recommends FB, NFLX, and TWTR. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.