It's been an exceptionally volatile year for the stock market, but that hasn't fazed young investors one bit. Robinhood, the online app best known for offering commission-free trades, fractional-share investing, and gifting free shares of stock to new members, signed up millions of new users in 2020. That's noteworthy because the average age of Robinhood's user base is only 31.

For months, Robinhood's leaderboard -- i.e., the 100 most held stocks on the platform -- hasn't changed all that much. But over the past couple of weeks, we've witnessed significant adjustments to what millennial and novice investors want to own.

Silver dice that say buy and sell rolling atop a digital screen showing stock charts and volume data.

Image source: Getty Images.

These top-10 holdings aren't going anywhere

Although the order has flipped around a bit, the five most held stocks on Robinhood have been in the top 10 for quite some time. As of this past weekend, this included the following stocks, ranked in order of popularity:

  1. Apple (NASDAQ:AAPL)
  2. Tesla (NASDAQ:TSLA)
  3. General Electric
  4. Ford
  5. American Airlines Group (NASDAQ:AAL)

Some of these are no-brainers. For instance, Apple has the most popular smartphone in the U.S. and should see its operating margins pick up as it proactively becomes a service-oriented company. Apple is also one of the most recognized brands in the world. It's a logical top holding that young investors can easily relate to.

Even though I strongly disagree with its current valuation, Tesla's popularity among millennials makes sense. Electric vehicles (EV) are the future of the auto industry, and Tesla has clearly identifiable first-mover advantages. The company is on pace to potentially top 500,000 EVs delivered in 2020, and its battery technology continues to lead its peers in both range and power.

The consistent top-10 holding that makes little sense is American Airlines. The airline industry is capital-intensive and produces meager margins, which should already be a red flag. What's worse is that American Airlines has buried itself in over $41 billion in debt. Even if it survives the coronavirus pandemic, this debt will strangle growth opportunities for the next decade.

A parent carrying an Amazon package under his arm while their child holds a door open.

Image source: Amazon.

These brand-name stocks are no longer top-10 holdings

The big surprises occur once you move beyond the top-five holdings. Three mainstay holdings in Robinhood's top 10 have fallen down the rankings.

Canadian marijuana stock Aurora Cannabis (NASDAQ:ACB), which was once the most held company on the entire platform, has fallen all the way back to the 15th spot on the leaderboard. Considering that Aurora's shares have declined by more than 90% since March 2019, an exodus by young investors was long overdue. Aurora has continually hurt its investors by issuing common stock and failing to meet its own forecasts of positive adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA). It's struggling mightily and should be avoided by investors.

Tech giant Microsoft (NASDAQ:MSFT) also finds itself on the outside looking in. Currently 13th on Robinhood's leaderboard, it's unclear why young investors have soured a bit on the company. Microsoft's fiscal first-quarter results showed it was business as usual, with a majority of the company's cloud offerings growing by a double-digit percentage from the previous year. Microsoft is generating insane amounts of cash flow and is aggressively reinvesting this cash into high-margin growth opportunities. In other words, it should probably remain a top holding by millennial investors.

Maybe the biggest shock of all is that Amazon (NASDAQ:AMZN) has fallen out of the top 10 (currently 12th). Like Microsoft, it's not entirely clear why millennials are piling into other companies instead of Amazon. According to an eMarketer report from March, Amazon was expected to control 38.7% of all online sales in 2020 and increase its share to 39.7% in 2021. That's roughly 33 percentage points higher than its closest competitor. Cloud infrastructure segment Amazon Web Services is also growing like a weed. It should help triple Amazon's operating cash flow within the next four years. 

A physician administering a vaccine to an elderly person.

Image source: Getty Images.

Here's the rest of Robinhood's new top 10

Following the top-five holdings mentioned earlier are Robinhood's remaining top-10 holdings (in order):

  1. Pfizer (NYSE:PFE)
  2. Carnival
  3. Delta Air Lines
  4. NIO (NYSE:NIO)
  5. Disney

Pfizer has quickly risen up the ranks in 2020 after developing a successful coronavirus vaccine with the help of BioNTech. The Pfizer/BioNTech vaccine (BNT162b2) delivered vaccine efficacy of 95% in phase 3 trials, which blew researchers' expectations out of the water. This vaccine was recently granted emergency use authorization by the U.S. Food and Drug Administration and should have a pretty clear path to billions of dollars in annual sales in 2021.

As you'll note, millennials really love auto stocks focused on EV production. NIO has rocketed up Robinhood's leaderboard throughout 2020 and found its way into the top 10. The China-based premium EV manufacturer is operating in the largest EV market in the world. It's seen its gross vehicle margin flip into the positive from the prior-year period. Admittedly, NIO's valuation is incredibly aggressive, given that it's on pace for an annual run-rate of only 50,000 EV deliveries. However, this doesn't seem to be fazing younger investors.

Millennials are taking big risks by betting on Delta Air Lines and Carnival, though. While coronavirus vaccines raise hopes of ending the pandemic, the balance sheets for most airline stocks and cruise companies aren't pretty. It could be years before we see travel and leisure demand return to anywhere near pre-coronavirus levels.

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.