I don't buy a lot of stocks. But with so many amazing businesses trading on the public markets, there are a lot that I want to buy. Many factors need to come together for me to press the buy button: the right allocation of paying myself first, an emergency fund, and funds available for investing. Plus, the stock has to meet my criteria

I love growth stocks. Not only because they usually offer the biggest reward for my investment, but because they are exciting. They typically make a big impact on the world, changing the way people think and operate. These are five stocks that are climbing up my prospective buy list, in no particular order: Fiverr International (NYSE:FVRR), Square (NYSE:SQ), Roku (NASDAQ:ROKU), Airbnb (NASDAQ:ABNB), and Upstart Holdings (NASDAQ:UPST)

A mother and daughter making piles of coins on a table.

Image source: Getty Images.

Fiverr: A better freelance model

There are several companies that service the freelance community and connect businesses with providers. Fiverr stands out for me because of its differentiated model of SAAP, or service-as-a-product. I've used freelance websites in the past when I was building up my financial writing portfolio. I love Fiverr's model, where sellers present their services as gigs, or packages with set prices for their work. That makes the purchase process easy and straightforward, and it's one of the reasons Fiverr has demonstrated explosive success.

Last year was an exceptional year due to the pandemic and stay-at-home orders. Revenue increased 77% year over year, gross margin widened, and the net loss was cut in half. Growth has decelerated into 2021 as people go back to offices, but it's still strong, with sales up 60% year over year in the second quarter, and an increase of around 50% expected for the full year.

The other reason I see so much potential for Fiverr is its focus on innovation. The company has rolled out many upgrades and additions to its services, including a premium fee-based seller's program, a training program for jobs directly with Wix.com and Salesforce.com, and a business program aimed at larger clients. Management sees a $115 billion addressable market, giving it lots of room to grow.

After huge gains in 2020, Fiverr stock is up an underwhelming 15% over the past year, only about half the gain of the S&P 500, and it's still trading at an enormous price-to-sales valuation of 26. Is there enough growth potential to justify that premium? I think this is a buy-and-hold situation, where investors will need to wait for the company to catch up to the stock price, and over time patient investors will see high gains.

Square: Financial services in one click

Fintech, or financial technology, has made strong inroads into just about every type of financial service available today. It's become popular because it simplifies many processes that are cumbersome in their traditional models, such as banking and stock trading.

When customers use Square's Cash App, they can perform a host of functions, including its original peer-to-peer payments and Bitcoin trading, with the click of a button. It's easy to see why this is attractive, and Cash App revenue increased 177% in the second quarter. Overall revenue, which includes the sellers business, increased 143% over that period.

As Square adds features to its Cash App, it drives higher engagement, higher sales, and higher profits. The company chartered a bank in March, which is the basis for its savings accounts, and will also provide the backbone of a new small-business banking platform for its sellers side. The opportunities are huge as it enters this new space. It's also expanding the sellers business, and it recently announced a deal with social media video company TikTok for business clients to feature shop pages in their TikTok videos.

Square has been a powerful investment, and its stock has gained almost 2,000% over the past five years. It trades at a huge valuation of more than 200 times trailing-12-month earnings, but it's still growing and has enormous potential.

People sitting at a table with computers wearing masks.

Image source: Getty Images.

Roku: Streaming is the new television

Who says people don't want to see ads on their streaming service? Despite the prevalence of paid streaming subscription companies such as Netflix and Disney's Disney+, Roku has created a niche of its own with its on-demand, ad-supported streaming site, the Roku Channel. According to its annual survey with the National Research Group, Roku is the No. 1 TV streaming site in the U.S. by hours streamed.

Advertising is the company's biggest growth driver as advertisers move their money over to streaming, and platform revenue increased 117% in the second quarter year over year. Player revenue, or sales from its devices, increased 1% as the company deals with supply chain issues. 

Roku is seizing the opportunity through the launch of Roku Originals, its own original content. It will produce more than 75 new pieces of content this year to compete with the leaders, and so far management says the response has been "overwhelming." The annual survey showed that 73% of responders said access to a new movie release is a reason they would try a new streaming service, and having fresh content is a way to get new viewers as well as more advertisers. As viewership and streaming hours grow, the company is unlocking a huge opportunity.

Roku stock is about flat year to date, and it's trading at a pricey valuation of 244 times forward one-year earnings. That's expensive, but I find the growth prospects compelling.

Airbnb: Custom travel experiences

Airbnb is all about what traditional travel is not: unique custom experiences, with every residence different. It can also be cheaper and provides a much wider assortment of rentals in terms of size, type, and location. And that's where it's challenging for hotels to compete, since Airbnb can expand its rental collection without laying a single brick.

That's why the company is demonstrating soaring growth, with a nearly 300% year-over-year sales increase in the second quarter, and a close to 200% increase in nights and experiences booked. That's way more than a pandemic rebound.

Management sees a $115 trillion addressable market, of which it has a fraction at $1.3 billion in second-quarter revenue. With its expanding list of vacation rentals and travel innovation, such as unique experiences, it has a path to gain greater market share. It's still posting a loss, but it narrowed in the second quarter, and as the company scales, its platform should do the heavy lifting while Airbnb turns sales into income.

Airbnb went public last year, and its stock is up about 18% from its initial public offering after falling from highs in early 2021. It trades at a P/S ratio of 23, making it expensive. But I think Airbnb has a huge growth runway and big potential for stock gains.

Upstart: Data-driven financing

Upstart is definitely in the running for the 2020 IPO with the biggest gains. The company provides a platform for banks to assess customer risk based on more than 1,600 data points, resulting in more approvals (71% of them instant) and less risk. 

The company says that 80% of Americans have never defaulted on a loan, but only half can get the credit they need based on traditional credit scoring systems. That's a losing situation for both customers and banks.

It's easy to see why Upstart's sales are skyrocketing. Revenue increased more than 1,000% in the 2021 second quarter, and net income increased to $37 million from a loss in the second quarter of 2020.

Upstart sees a huge opportunity, with more than $4 trillion of credit issued from June 2020 to June 2021, according to TransUnion. There were $635 billion in loans during that period, and the company recently entered the auto loan space with Upstart Auto Retail. It's already operating in 47 states, and it can add huge volume to Upstart's platform.

As of the time this was written, the stock has gained more than 950% since its IPO less than a year ago. That gives it a forward P/E of 223, a lofty valuation. But there is so much more room to grow, and investors shouldn't make the mistake of thinking the gains are over.

I really like all of these stocks and their growth prospects. They're all fairly expensive, but they all meet customer needs in a changing environment. When I'm ready to buy, it will be hard to choose one.

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.