Growth stocks have been crushed over the last year, but just as they ran too high during the pandemic, they now seem to have fallen too far during the sell-off.

Valuations have crumbled, and investors have gone from thinking industries like e-commerce would have limitless growth to believing that they're dead. That sell-off has created a buying opportunity, and two stocks down big that look especially promising are Roku (ROKU 0.15%) and Shopify (SHOP -2.37%).

Here's a closer look at why each of these growth stocks holds significant long-term promise despite being down more than 50% over the past 12 months.

1. Roku: Streaming is still growing

Roku stock is down a whopping 89% from its peak in 2021, as seemingly everything has gone wrong for the leading streaming platform.

First, subscriber growth in services like Netflix seemed to hit a ceiling after a surge in growth earlier in the pandemic. The ad market also shriveled as brands are preparing for a recession and cutting spending. In fact, the slowdown is bad enough that Roku actually forecast a decline in revenue in the fourth quarter.

Roku has also swung from profits in 2021 to sizable losses as the company stepped up its investments in the business just as revenue growth started to slow.

However, it's a mistake to think the Roku growth story is dead. In fact, the company continues to grow users and viewing time, which is a sign that demand for its service remains strong.

Earlier in January, the company said it had topped 70 million active accounts globally, adding 9.9 million in 2022, more than the 8.9 million it gained in 2021. The company also said streaming hours increased 19% in the year to 87.4 billion, showing that Roku users are spending more time with the platform.

Roku's business is centered around advertising. It takes a 30% share of ad inventory from its streaming partners, and with several legacy media companies having recently launched streaming services and Netflix and Disney recently adding advertising tiers, Roku should get some significant tailwinds over time.

Despite the current headwinds, Roku's long-term growth still looks promising, and the stock should recover once the ad market picks up.

2. Shopify: E-commerce will rebound

Much like Roku stock plunged on weakness in the streaming industry, so has Shopify plunged due to the slowdown in e-commerce.

Shares of the e-commerce software leader have tumbled after surging on strong growth during the pandemic. Revenue growth has slowed as its profits have turned into losses, and it has seen a stretched valuation, which was up to a price-to-sales ratio over 50 at one point during the pandemic.

Shopify is far from the only e-commerce stock that's struggling lately. In fact, most have experienced the whipsaw effect of a boom and bust during the pandemic, including Amazon, Etsy, and Wayfair.

Despite those headwinds, the long-term opportunity for Shopify is still intact. It's the clear leader in e-commerce software, and it's still outgrowing the industry, posting 21% constant-currency growth in gross merchandise volume during the Black Friday weekend. In addition, retail sales volume should continue to shift from brick-and-mortar stores to the online channel over time as delivery gets faster and more convenient and finding the product you want gets even easier.

As a software company, Shopify also has the capability to be highly profitable once the business scales and starts to mature, though the company has spent aggressively on growth throughout its history. For example, it spent $2.1 billion last year to acquire Deliverr, a fulfillment technology company, to beef up its own fulfillment network to better compete with Amazon. In fact, Shopify and Amazon increasingly appear to be on a collision course as Amazon as expanding its Buy with Prime program to all eligible merchants at the end of January, posing a potentially serious threat to Shopify.

However, if Shopify can fend off that threat, its growth should accelerate as it moves past the difficult comparisons from the pandemic, and it should get tailwinds from the economic recovery whenever that happens.

Expect Shopify to continue to develop its fulfillment network, and as it does, the platform will become more attractive to merchants and even more competitive with Amazon.