September has historically been the worst month for stocks. Investors often take profits on their summer gains, funds sell their weaker stocks as tax write-offs, and those sales trigger additional waves of selling. This September doesn't feel much different. As of this writing before markets open on Sept. 9, the S&P 500 has declined by about 5% for the month as the tech-heavy Nasdaq dropped nearly 10%.

However, long-term investors should embrace these sell-offs as buying opportunities, especially in high-growth tech stocks that previously seemed too hot to handle. Here are three tech stocks I'll eagerly buy if the market crashes this month: (CRM -0.57%), Sea Limited (SE -2.20%), and (JD 0.20%).

Panic-inducing headlines about the coronavirus clipped out and mixed with hundred-dollar bills.

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1. Salesforce

Salesforce's stock hit all-time highs in the week following its second-quarter earnings report in late August. Investors cheered as the cloud services provider generated over $5 billion in quarterly revenue for the first time ever, its billings growth accelerated, and its adjusted operating margin hit a record high. It also raised its revenue, operating cash flow, and earnings guidance for the full year.

Those blowout numbers indicated Salesforce's core businesses -- which help companies maintain customer relationships, sales and marketing campaigns, and analyze data -- remain well-insulated from the COVID-19 crisis. The pandemic also boosted demand for its tools in the remote work and online education markets.

Salesforce's services automate business processes and reduce an organization's dependence on human employees, and demand for those tools will likely climb as companies cut costs and streamline their businesses. That secular trend won't be significantly disrupted by recessions, and Salesforce's scale and market-leading position in the customer relationship management (CRM) market make it a solid growth stock for long-term investors.

Salesforce's stock has declined about 15% from its post-earnings peak, and its forward P/E of 80 looks reasonable compared to those of other comparable cloud stocks with triple-digit multiples. If the sell-off deepens, investors should consider scooping up shares of this cloud king, which expects its revenue to rise 21%-22% this year, with 24%-25% growth in non-GAAP earnings.

2. Sea Limited

Sea Limited's stock also hit an all-time high after the Southeast Asian tech company posted its second-quarter earnings. The robust growth of Sea's profitable gaming business, Garena, offset the ongoing losses from its unprofitable e-commerce unit, Shopee. The COVID-19 crisis also lit a fire under both businesses as more people stayed home, played more games, and shopped online more frequently.

A young man plays a mobile game on a smartphone.

Image source: Getty Images.

Many critics, including myself, once believed Sea's e-commerce losses would constantly overwhelm the gaming unit's gains. However, Sea's first-party battle royale game Free Fire exploded in popularity and surpassed Tencent's (TCEHY 0.10%) PUBG Mobile as the world's most downloaded mobile game last year, according to App Annie. Free Fire's growth reduced Sea's dependence on licensed games and indicated it could consistently subsidize the growth of its e-commerce unit with its gaming profits.

Sea is only profitable on an adjusted EBITDA basis, and its GAAP losses are still widening. But it won't run out of cash anytime soon, thanks to a recent $1 billion debt offering, and it could eventually narrow its GAAP losses by gradually reducing its stock-based compensation expenses.

Sea hasn't provided any guidance for the full year, but Wall Street expects its revenue to rise 81% this year as its GAAP earnings stay in the red. Sea's stock might seem pricey at 13 times this year's sales, but it's already retreated over 15% from its post-earnings peak, and it remains more cheaply valued than many other high-growth tech stocks.

3., China's largest direct retailer and second-largest e-commerce company, also crushed analysts' expectations with its second-quarter earnings report last month. Its revenue grew year-over-year at its fastest rate in 10 quarters, its growth in customers accelerated, and its adjusted operating margin expanded from a year earlier.

JD's top-line growth was driven by its expansion into lower-tier cities, the growth of its online grocery business, and robust sales throughout its 618 Shopping Festival in June, while the expansion of its first-party logistics platform as a service for external customers reduced its fulfillment costs and boosted its margins. JD also continues to expand its ecosystem with JD Health, which offers telehealth and online pharmacy services, and JD Cloud, which provides cloud infrastructure services to enterprise customers.

JD didn't provide any guidance last quarter, but analysts expect its revenue and earnings to grow 30% and 51%, respectively, this year. Those are high growth rates for a stock that trades at less than 40 times forward earnings.

JD's stock recently pulled back slightly with the broader market, but it remains up more than 20% over the past month. If JD gets tossed out with the bathwater in a broader market sell-off, I'll happily add more shares to my existing position, which I started back in early 2018.