For many investors, becoming a millionaire is their key financial goal. Having a net worth of $1 million puts you well into the upper crust of the American population, and more importantly, it gives you the financial flexibility to take control of your life and do the things you want to do.

Saving and investing to reach the $1 million mark takes time and effort, however. If you earn an 8% return annually -- which is consistent with what the stock market has done over the long haul -- it'll take you roughly 40 years investing $300 a month to become a millionaire.

That's why many investors look at individual stocks to try to beat the stock market. If you can boost your average annual return to 10%, it'll knock more than five years off the time it takes you to become a millionaire. A 12% return would shorten it by 10 full years, while an extremely ambitious 15% target could make you a millionaire in 25 years -- all with just a $300 monthly investment.

The kind of stocks that can beat the market typically have strong growth prospects and are looking to take advantage of profitable trends. The three stocks you'll find below all have the high-growth potential that wannabe millionaires need. While there's plenty of risk involved in each of them, they could play a vital role in getting you to your goals.

1. Opendoor Technologies

Opendoor Technologies (OPEN) is new to the stock market. It went public through a special purpose acquisition company merger in late 2020. The company stands at the intersection of technology and real estate, with its iBuyer platform seeking to disrupt the way people buy and sell their homes.

Rather than engaging in a lengthy process of listing, seeking offers, negotiating, investigating, and closing on a home, Opendoor makes offers directly to would-be sellers in dozens of large markets across the nation. People can use the Opendoor platform to complete transactions in days rather than months.

Person carrying box amid lots of moving activity around a garage and house.

Image source: Getty Images.

Opendoor has gotten off to a strong start, but it has ambitious plans to grow. It's looking to enter nine more new markets by the end of 2021, with the eventual goal of broadening its network to 100 of the nation's largest areas.

The company is also seeking ways to increase its market share, as well as offering ancillary services like mortgages. With so many people right now looking at opportunities to change their lifestyles, real estate markets are red-hot -- and the need for the flexibility that Opendoor's iBuying service offers is greater than ever.

After rising sharply following its going-public merger, Opendoor has fallen by more than half from its all-time highs. That gives interested investors a great opportunity to put their money to work.

2. Fiverr International

The gig economy is growing fast, and many workers who are reluctant to go back into a regular office environment are seriously looking at freelance opportunities. Fiverr International (FVRR -1.17%) has a platform that connects workers with tech and other in-demand job skills with companies seeking to put their services to the test, and it's made a lot of money by building a reputation that both buyers and sellers can appreciate.

Fiverr has capitalized well on the opportunities in the job market. In its most recent quarter, Fiverr's revenue doubled from year-ago levels, as the company brought in 56% more active buyers and saw them spend an average of 22% more on freelancer services. Fiverr also expects continued healthy sales growth in 2021 and beyond, as the digital transformation across the economy favors the concentration of workers that the gig-economy platform has attracted.

Fiverr's shares soared about eightfold in 2020, but you can now pick up the stock at a nearly 40% discount to where it traded at its recent highs in February. With years of growth ahead, Fiverr looks like it will have a long runway to success.

3. Piedmont Lithium

Lastly, electric vehicles (EVs) are all the rage, and a host of companies in the EV space are looking for ways to revolutionize the auto industry. Battery technology plays a key role in those advances, and that's created unprecedented demand for the lithium that goes into most EV batteries right now. Many lithium producers are in foreign countries like China, but Piedmont Lithium (PLL) is looking to bring a more reliable source of lithium available to EV manufacturers in the U.S., Europe, and other areas of the world.

Piedmont is developing a lithium quarry in North Carolina as part of its plans to create a fully vertically integrated business operation. By bringing together the equipment and facilities not just to extract lithium from the earth but also to process it into a form that major automakers can use, Piedmont has aspirations to solve supply-chain challenges plaguing many companies in the industry. The lithium specialist has already signed a major supply agreement with industry leader Tesla (TSLA -3.40%), and Piedmont has high hopes for additional deals once its efforts are closer to completion.

The EV space has been highly volatile for investors, and Piedmont's stock is down almost 25% from its best levels earlier this year. With the world's appetite for lithium only growing, Piedmont stands to see big gains if it can execute on its opportunity to become a major supplier to the world's best EV companies.

Don't settle for less

Becoming a millionaire might seem impossible, but it's not. It will take time and effort, but strong-performing investments can help make it easier. With as little as $300 a month, you can start now and put in motion your plans to reach the $1 million milestone.