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The ride-sharing industry is growing at a heady pace, but thus far, if you wanted to get a piece of the action, you either had to be a rich venture capital type, a large company, or...well, a driver. But with both Uber and Lyft (and possibly China's Didi Chuxing) rolling toward IPOs this year, investors will have an opportunity to profit from these transportation disruptors. There are also a lot of possibilities for the transportation-as-a-service segment more broadly. It all combines into an evolving picture that analyst Aaron Bush will be observing with interest over the next year.

On the other hand, there's the social media sector, which his comrade in arms Matt Argersinger has under scrutiny for less upbeat reasons. After years of seemingly unstoppable growth, Facebook (NASDAQ:FB) and its rivals may have painted themselves into a bit of a corner. Between the privacy concerns, the information security issues, and the increasing levels of platform abuse by malefactors large and small, a whole lot of people are beginning to question how they use social networks. And that could be bad news for growth and profitability. In this segment from the Motley Fool Money podcast, host Chris Hill talks with Argersinger and Bush about what they see coming down the pike for both industries, and how they might meet their challenges.

A full transcript follows the video.

This video was recorded on Jan. 4, 2019.

Chris Hill: Let's get to our 2019 preview. Aaron, I'm going to start with you. What is one industry you're going to be watching this year?

Aaron Bush: I'm really interested to be watching the ride-sharing industry. With Uber and Lyft, and maybe even Didi, which is in China, IPO-ing in 2019, it's really exciting that public market investors will finally have access to this new, massive, quickly growing industry. I'm excited to see what the numbers look like. They probably won't be great from a profitability perspective. But thinking about transportation as a service, and what that means beyond just ride-sharing, what it means for logistics with food, and are they going to buy more bike and scooter companies? That type of thing. I'm really interested to hear more about that longer-term game plan. We'll learn a lot about that in 2019.

Hill: Matty, what about you?

Matt Argersinger: It's always interesting, but I think especially so this year, I'm going to be watching the social network, social media space. We're already seeing for the first time ever a real, legitimate slowdown in user growth and usage rates, especially if you look at the core Facebook platform. My questions are, how does Facebook, how does Twitter, how do these companies solve for all the privacy risks that people seem to be somehow aware of these days that they weren't aware of years before? How do they prevent all the vile and deceptive behavior without damaging free speech and freedom of expression on the platforms? These are big challenges. Throwing money and bodies as we've seen Facebook do, I'm not sure that's going to solve it. It's going to take a lot of innovation. I don't doubt Facebook and Twitter can do it, but I think there's a real chance we actually see a tipping point in 2019 where the powerful network effect that has sucked in so many users over the years to these platforms starts to weaken, and we start to see meaningful declines in time spent on the platforms. I think it'll cause a reset of the businesses.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.