Based on its stock price the past few days, it appears most investors and analysts are content with Facebook (NASDAQ:FB) dropping a total of $19 billion for instant-messaging app WhatsApp. After initially jumping about 5% in the days immediately following the announcement -- from $67.30 a share the day before the news broke to a high of $70.78 a share on Feb. 24 -- Facebook's share price seems to have settled into a comfortable trading range.

What's impressive is that Facebook's been able to maintain much of its share-price increase since the WhatsApp announcement, even after the initial euphoria wore off. That's good news for Facebook shareholders, but is it warranted? Dropping $19 billion -- of which $4 billion is in cash and the remainder in restricted and unrestricted stock -- for a company that makes virtually no money, and doesn't appear to have any definitive plans to do so anytime soon, is a bit of a head-scratcher, to say the least.

What's with WhatsApp?
With over 450 million monthly active users (MAUs), WhatsApp is the leading instant-messaging (IM) app in the business. According to Facebook's press release, 70% of those 450 million plus MAUs use WhatsApp on a daily basis. Facebook CEO Mark Zuckerberg also noted that WhatsApp is adding about 1 million users daily and is "on a path to connect 1 billion people" making WhatsApp "incredibly valuable." But $19 billion?

The user numbers for WhatsApp are impressive. To give you some perspective, high-flying Twitter (NYSE:TWTR), with a stock price that has more than doubled since its IPO late last year, has a mere 241 million users as per its 2013 Q4 earnings announcement, and the rate of growth is slowing. Even with its stock price easing significantly the past month, Twitter is still valued at $30 billion, as measured by market cap. So, maybe $19 billion for WhatsApp isn't so crazy after all.

WhatsApp is growing by leaps and bounds, it immediately expands Facebook's mobile solutions -- a well-known objective of Zuckerberg and team -- and gives it more access to markets outside North America, a big part of WhatsApp's user base. What's not love about WhatsApp? A few things.

The concerns are many
Unlike ridiculously overvalued Twitter, WhatsApp has virtually no revenues. Twitter's revenues certainly don't warrant its stock price, not by a long shot, but it did generate $665 million in revenue last year, and expects that figure to nearly double in 2014. Profits will be a while coming, but at least there's something there for investors to hold onto.

As for WhatsApp, charging users $1 a year, after a complimentary first year, isn't going to cut it when you consider its $19 billion price tag. Facebook will monetize the service using a similar formula it employs itself: use massive amounts of user data to target ads, right? Not according to WhatsApp or Facebook. The IM service will remain ad-free, as per its CEO and co-founder Jan Koum. If not ads, then how does Facebook monetize the service to get a return on its investment?

Instant messaging, at least as it pertains to WhatsApp, doesn't appear to instill a sense of user loyalty, as evidenced by last weekend's three and a half hour server shut down. In the time it took WhatsApp to get its servers back online, its two primary competitors, Line and Telegram, gained two million and five million new members, respectively. With virtually no revenues and promises to its users that ads won't be included in the service going forward, what is Facebook buying if not a worldwide mobile-user base? And if those same users leave at the drop of a hat, as they appeared to have done last weekend, will they really be worth $19 billion at some point in the future?

Final Foolish thoughts
Another question is how many of WhatsApp's users are already Facebook users, too? With more than 1.2 billion Facebookers around the globe, it's safe to assume that at least some of the WhatsApp community is already on Facebook. Which leaves WhatsApp with virtually no revenues, an iffy user base, and promises from all those involved to not monetize the service via ads. Those are legitimate reasons to question Facebook's $19 billion deal.

The concerns are many, but Facebook's been down this path before. Remember a year ago? Facebook stock was sitting at $27.25 a share in large part because it wasn't monetizing its services fast enough, and its mobile strategy was just getting implemented. Zuckerberg addressed those concerns, in a big way. And based on the market's reaction, it seems many investors are inclined to give Facebook some time to see what it can do with its new $19 billion toy. With its successful track record, Facebook's earned the benefit of the doubt. For now.

Tim Brugger has no position in any stocks mentioned. The Motley Fool recommends Facebook and Twitter. The Motley Fool owns shares of Facebook. 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.