There are plenty of investing strategies you can use when choosing a stock to buy. Some investors may be looking for more stability, others want solid dividends for years to come, and others may be looking for companies that are growing at breakneck speeds.

For investors looking for fast-paced growth, which may also come with a bit of volatility, Okta (NASDAQ:OKTA), Shopify (NYSE:SHOP), and Square (NYSE:SQ) should be on your short list. Here's why. 

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Okta

Unless you're a tech investor, there's a good chance that you haven't heard about Okta. The company is in a fast-growing, but still mostly unknown, market called identity and access management. Okta creates software that companies can use to create well-defined parameters to give users access to online information. 

Okta's technology helps companies create a gatekeeper system that makes it easy to manage existing users and add new ones. Okta is a leader in the fast-growing identity management space, which will be worth $23 billion by 2025, and the company's sales growth has helped push its share price up 335% over the past three years. 

Okta's revenue increased by 49% in the most recent quarter, and the company continues to build its subscription sales, which jumped 51%. That's impressive enough on its own, but there's likely more growth ahead for the company. Okta's management expects full-year revenue to reach $563 million at the high end of its guidance, which would represent 41% sales growth compared to the previous year.

Shopify 

Another growth stock that investors should be keeping an eye on is the e-commerce platform company Shopify. The company has a host of services for businesses of all sizes, including website and online store setup, as well as services for managing payments and shipments. Shopify has more than 800,000 businesses using its platform, and in the most recent quarter, the company's sales jumped 48% from the year-ago quarter.

What makes Shopify's stock uniquely compelling is the fact the company still has a lot of potential to grow as the e-commerce market takes shape. For example, only 11% of all retail sales occurred online in the U.S. this year, and the global e-commerce market will reach an estimated $6.5 trillion in 2022.

So even though Shopify's sales are booming and the company's share price has skyrocketed 330% over the past several years, the fact that e-commerce is just getting started means that there's still plenty of runway left for Shopify.

Square 

Investors looking for a company that's on the cutting edge of digital payments need to give Square strong consideration. Not only is this payment processing company increasing sales -- revenue jumped 44% in the most recent quarter -- but the amount spent on the company's platform continues to climb as well. The company's gross payment volume (GPV) -- the amount spent through Square's platform -- in the second quarter increased 25% from the year-ago quarter.

Square is benefiting from the growth of e-commerce (see Shopify section above) and also from the proliferation of digital transactions made through smartphones. Square's peer-to-peer payment app, Square Cash, allows users to pay each other, and the app is already a $500 million business for Square.

As digital payments continue to grow, Square is already poised to benefit through its payment processing hardware and software for business and through the Cash App. With digital payments expected to become a $7.6 trillion market by 2024, Square is sure to cash in as this market expands.

High growth doesn't mean short-term perspective

While each of these companies is growing quickly, that doesn't mean that investors should ride a short wave of gains and then hop off. These companies are likely to experience some volatility because they're still in high-growth mode, which means that you may need to ride out some share price dips along the way. For example, Shopify's stock is down 26% over the past three months. But patient investors will likely be rewarded as Okta, Shopify, and Square continue to grow into their respective markets.