Since the beginning of the year, the stock market has experienced more than a dozen single-day drops of 1% or more, and a fair number of sharp rises too, but even with that growing volatility, the S&P 500 remains up about 12% over the past 12 months.

Returns on that level are certainly respectable, but a handful of technology companies have done four or five times as well over the same period. For example, Shopify (NYSE:SHOP), Okta (NASDAQ:OKTA), and PayPal Holdings (NASDAQ:PYPL) are all up 50% or more over the past year. Let's take a quick look at what's driving the growth of each company, and why investors could expect more good things from them. 

Shopify: Up 68% over the past 12 months

Shopify sells its e-commerce platform and services to businesses of all sizes, allowing them to get their own online stores up and running, and make sales on social media platforms and Amazon. It has grown its client base by about 146% over the past two years, and now, more than 600,000 business use its platform.   That rapid pace of customer growth has powered revenue gains that hit 71% in the fourth quarter, and management is guiding for a 45% revenue increase for 2018.

The company has forged strong relationships with Facebook and Amazon; Shopify merchants can sell their products on both companies' marketplaces. Its moves to incorporate these platforms into its own services demonstrate Shopify's ability to adapt amid an ever-changing e-commerce environment. 

Investors should be aware that Shopify's shares are priced at a hefty premium of about 250 times its estimated forward earnings. But it's only beginning to tap into a rapidly growing market, and there's plenty of opportunity ahead as e-commerce draws an ever-greater fraction of our shopping dollars. Online sales in the U.S. were $385 billion in 2016, and they're expected to reach $632 billion just two years from now. If Shopify keeps expanding its client base and growing the volume of sales on its platform, the company should be able to justify the optimism built into its current stock price.

Okta: Up 64% over the past 12 months

Okta helps companies both large and small manage logins for employees. Its services can be used to control individual workers' access to files on internal corporate networks, and, with one login, supply simultaneous credentials for multiple third-party services. For example, some enterprises use Okta to simplify giving their employees access to Adobe's Creative Cloud services.

Okta went public in April 2017, and its share price generally tracked the S&P 500 until February, when it skyrocketed 31% following the company's announcement of its preliminary fourth-quarter results. Sales for the period increased by 59% year over year, and Okta's subscription revenue climbed 64%.

That growth has been fueled in part by its ability to bring in high-end customers. The number of clients paying Okta $100,000 annually rose 56% in the most recent quarter, and that group now includes large businesses such as Farmers Insurance and JetBlue.

This is still a young and growing company, which means it's likely to experience more share price volatility. But Okta is building a strong position in the growing identity and access management (IAM) business, which will be worth an estimated $20.8 billion by 2022.

PayPal: Up 55% over the past 12 months

PayPal's share price has for the most part climbed steadily over the past year, and though it fell a bit after eBay announced it was ending its primary payment provider relationship with its former subsidiary, there's still a lot for shareholers to be optimistic about.

Revenues grew by 24% to $3.69 billion in the first quarter, and PayPal's GAAP earnings per share jumped 33% year over year to $0.42. The company added an impressive 8.1 million active accounts in the quarter, an increase of 35% from the year before, and its total payment volume (TPV) reached $132 billion in the quarter, a 32% year-over-year jump.

Investors have responded positively to PayPal's growth, but it certainly has further opportunities ahead. Its peer-to-peer payment app, Venmo, processed more than $12 billion worth of transaction in the quarter, as total P2P volume grew 50%. To put the growth opportunities ahead for Venmo in context, consider this: In 2017, the total of all P2P transactions exceeded $120 billion; that volume is forecast to hit $244 billion by 2021.

Lots of potential, but remember this

While it's exciting to see a company's stock price take off -- especially if it's in your portfolio -- investors should always remember the adage that past performance does not necessarily predict future results.

I believe PayPal, Okta, and Shopify have substantial opportunities that should help them to continue growing, but investors considering buying shares should also be aware of some of the key risks for each company.

For example, Okta is young, and it lacks an economic moat. While it's growing now, a competitor could start doing exactly what Okta's doing and begin stealing away customers. Similarly, Shopify has experienced meteoric customer growth, but if the company finds itself having difficulty retaining those customers, it could face some big hurdles ahead. PayPal is likely in the strongest position of the three, but even it suffered a stock price slide when eBay said it was shifting to European-based Adyen as its primary payments processor.

In short, remember to take a long-term perspective for your investments; don't just buy a stock because its share price is skyrocketing. 

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Chris Neiger has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Adobe Systems, Amazon, Facebook, Okta, PayPal Holdings, and Shopify. The Motley Fool recommends eBay and JetBlue Airways. The Motley Fool has a disclosure policy.