Although the S&P 500 climbed more than 4% in March, some stocks had an awful month as investors moved away from growth stocks and toward value buys. The ARK Innovation ETF, which focuses on some of the most promising growth investments, declined by 8% while the Vanguard Value ETF outperformed the markets, rising by more than 6%. But that doesn't mean investors should stop buying growth stocks, especially those that still have some great prospects.

Three of March's beaten-up stocks that are still good buys today are Moderna (MRNA -8.05%)Snap (SNAP 0.66%) and Roku (ROKU -0.55%). Here's a closer look at how badly they've done of late and why they're still worth investing in right now. 

Investor with his hands on his head as a stock falls.

Image source: Getty Images.

1. Moderna

Shares of Moderna slipped to less than $120 late in March -- a nearly three-month low for the healthcare stock. It's possible that the company's year-end results, which Moderna released on Feb. 25, played in a role in the stock's recent activity. For the fourth quarter (ended Dec. 31, 2020), the company generated $570.7 million in revenue, which was more than 40 times the $14.1 million it posted in the prior-year period. But despite the boost in grant revenue and Moderna now reporting product sales, its net loss of $272.5 million was more than double the $123.3 million loss it incurred a year ago. 

However, that shouldn't be a reason for investors to sour on the company, as there are plenty of reasons to remain bullish on the stock. In mid-March, Moderna announced that phase 1 trials were underway for its new COVID-19 vaccine, mRNA-1283, which is stable in a refrigerator. Its current vaccine, mRNA-1273, needs to be stored at much colder temperatures (-4 degrees Fahrenheit). And with countries backing away from AstraZeneca's vaccine due to safety concerns, Moderna could capture more of the market. This year, the company anticipates that it will generate up to $18.4 billion from vaccine sales. 

Although some investors may be concerned about Moderna's mounting losses, when looking at its forward price-to-earnings ratio, the stock is trading at less than six times its future earnings. That's a cheap valuation when you consider that investors are paying more than 27 times earnings for the average stock in the Health Care Select Sector SPDR Fund. Moderna fell more than 15% in March, and buying the stock on the dip could be a great move as there is still lots of growth left for the company.

2. Snap

Snap's stock tumbled by more than 20% last month. It's a bit of a surprise given that Snap, the company known for its popular camera app, stated in March that it can generate 50% revenue growth for multiple years. And that's with the company just growing its ad business. That's a big projection given that in 2020 the company's sales of $2.5 billion grew at a rate of 46%. Posting multiple years of high growth is no easy task, and the danger is Snap could be setting itself up if it falls short of those extremely bullish projections. Investors may also be concerned that despite the recent growth, Snap is still deep in the red. Its net loss of $944.8 million last year wasn't a whole lot better than the $1 billion loss Snap posted in 2019.

Profitability may still be a question mark, but if Snap can achieve those impressive sales targets it could be an excellent reason to remain bullish on the stock. Investors have shown a willingness in the past to look past a lack of profitability in exchange for some solid sales numbers, and that's why Snap may still be a good buy over the long term. While its price-to-sales (P/S) multiple of 30 looks high right now (the average stock in the Technology Select Sector SPDR Fund only trades at a multiple of six), that can quickly come down if Snap generates the sales it is expecting over the coming years.

3. Roku

Another stock that struggled in March was Roku, falling by 18%. As is the case with Moderna and Snap, there wasn't a key development that suddenly made Roku a worse buy; the company was coming off a strong year-end performance. It released its latest results on Feb. 18, and net sales of $1.8 billion for all of 2020 grew 58% year over year. Its streaming hours of 17 billion for the last three months of the year were also 56% higher than a year ago.

One concern may be that as more people are vaccinated and the economy starts opening back up, consumers will not use streaming devices as often because they will be too busy traveling and making up for lost time due to the pandemic. And while those concerns are valid, they are short-term problems. I wouldn't be worried about the business over the long haul as it continues to expand its growth opportunities.

In January, it acquired content from Quibi, which features short episodes of 10 minutes or less. That will add some valuable ad-supported content for Roku, which already has a free channel that it offers to customers. The company also began selling the Roku Streambar and a new ultra device last year, both of which are at significantly higher price points ($99-$180) than its streaming sticks ($50 and under).

With new products and more content, Roku still has some attractive growth prospects ahead. Its P/S multiple of 23 is a bit high if you're comparing its valuation to the SPDR S&P 500 ETF Trust, where stocks trade at just three times their sales. However, Roku may be worth the premium given its incredible growth, the potential it still possesses, and the company's strong position in the industry -- it captured a 38% share of the U.S. smart TV market last year.

If you're looking for a top growth stock to buy at a discount, Roku is one of the better options available right now.