Last year is a hard act to follow for most investors, but there are already nearly 100 U.S. exchange-listed stocks with market caps above $300 million that have more than doubled in 2021. It will be a challenge for most of them to hold on to their scintillating gains, but let's look at some of the names that could just be getting started.

Upstart Holdings (UPST 0.96%), Funko (FNKO 2.83%), and AMC Entertainment Holdings (AMC 8.23%) have the right ingredients to keep the gains coming. Let's look to see why these three stocks could double again in 2021.

A man celebrating with fists raised in the air.

Image source: Getty Images.

1. Upstart

Loaning money to folks with less than stellar credit scores has historically been a recipe for disaster, but it's also a niche that Upstart is upending by using artificial intelligence to make better bets on the underserved in the personal lending market. Upstart saw its revenue climb 42% last year, and things are about to get even better.

Its guidance calls for revenue to soar 115% this year. An acquisition that should close in June for Prodigy Software will find it expanding its business into the auto loan market, which is ripe for an AI-fueled disruptor. More data to munch will naturally make the tech-savvy company even smarter.

The stock isn't cheap after nearly tripling this young year. Analysts doubled their forward profit targets after last month's blowout report, but we still find Upstart trading for more than 200 times this year's projected earnings and over 100 times next year's forecast. Triple-digit earnings multiples aren't the norm in the stodgy financial services game. But with the stock already more than 30% below its March high, this is a good opportunity to pick up a company that is about to step hard on the accelerator pedal in the latter half of this year.  

2. Funko

Your collection of Funko vinyl figures and bobbleheads isn't a passing fad. The stock has more than doubled this year on the strength of a surprising financial turnaround and its decision to hop on a hot digital craze.

Funko was posting double-digit annual revenue growth for at least four years before the pandemic shriveled up demand for its licensed collectibles. Revenue plummeted 18% for all of 2020, but analysts weren't expecting sales growth to turn positive over the holidays. The $226.5 million it posted on the top line for the fourth quarter was just a 6% year-over-year increase, but Wall Street pros were bracing for an 8% decline. Weak international sales were lifted by a head-turning 18% surge in the U.S. market. Funko's quarterly profit of $0.24 a share also blew past the $0.14 that analysts were targeting.

The next step up for Funko came when it announced a deal to acquire a majority stake in TokenHead, a leading platform for showcasing and tracking non-fungible tokens (NFTs). TokenHead's flagship TokenWave app attracts more than 100,000 daily visitors checking out its listings of more than 10 million blockchain-backed tokens. With stimulus checks already being earmarked for more Funko keepsakes, the company is now in prime position to be a major player in digital collectible assets. 

3. AMC Entertainment

Upstart and Funko are two companies in the early stages of growth spurts, but AMC is one that most investors associate with the endgame for a fading industry. Even before the pandemic, folks were shying away from a night at the movies. AMC revenue was flat in 2019, and that was with the country's leading multiplex operator gaining market share as domestic box office receipts declined 5% that year. 

The pandemic has been brutal to AMC and its smaller peers, and the near-term outlook is hairy. Consumers and movie studios have embraced digital delivery, and neither party has the patience for traditional theatrical-release windows where content would be shown exclusively on the big screen for a couple of months before hitting other distribution platforms. 

However, we have seen movie theater crowds surge in international markets that are further along the COVID-19-tackling curve. With 99% of AMC locations now open, studios are ready to trust exhibitors with hot products that they've been delaying during the lull. With an industry shakeout already eliminating some of its competition, AMC is going to have a big summer this year as folks begin to rediscover social settings. 

Upstart, Funko, and AMC Entertainment have more than doubled in 2021. The catalysts are there to potentially make them double again before the year is done.