Robinhood is a popular trading platform that often serves as a barometer of what's hot and what's not on the markets. Stocks that are among the most popular on Robinhood come from a variety of industries and risk levels, but most are primed for serious growth.

However, there are a couple of surprising omissions from the Robinhood Top 100, a continuously updated list of the most popular stocks on the platform. Teladoc Health (TDOC 6.69%) and Shopify (SHOP -1.11%) are two high-growth stocks that I'd expect to be popular among Robinhood investors, especially since both companies doubled their sales over the past two years and Robinhood captures a large millennial audience that follows burgeoning businesses.

1. Teladoc

Teladoc Health is currently the 212th most popular stock on the platform, according to Robintrack, which tracks the popularity of stocks on Robinhood. That's a surprise considering the virtual healthcare platform's success this year -- its share price is up more than 120% year-to-date. Teladoc's service allows patients with or without insurance to access a doctor via virtual visits, demand for which has soared amid the COVID-19 pandemic, as people shelter at home and avoid in-person trips to the doctor's office.

Excited investor.

Image source: Getty Images.

Teladoc recently released its second-quarter numbers, reporting year-over-year sales growth of 85% for the three-month period ending June 30. The number of virtual visits conducted through the platform grew from 908 million in the year-prior to nearly 2.8 billion, an incredible 203% increase. There's still a lot of room for the company to grow, especially as COVID-19 remains a serious public concern. The challenge for Teladoc is to continue growing at more than 80% year-over-year. While that growth rate is probably unsustainable over the long term, it is not unreasonable for double-digit growth to continue indefinitely given the pandemic and patients' desire to minimize unnecessary travel.

The company has also been making headlines this summer. On August 5, Teladoc announced its planned $18.5 billion merger with Livongo Health, which is sure to drive even more growth in the future. Livongo, which is ranked at #178 on Robinhood and ahead of Teladoc, focuses on treating people with chronic conditions, specifically diabetes. Through its network of devices, patients have the ability to share their glucose readings with family members and health coaches. The deal extends Teladoc's reach into forming patients' day-to-day health habits and opens up a new consumer base. The merger is still subject to shareholder approvals but the companies expect the transaction to close by the fourth quarter. 

Teladoc has had a banner year thanks to the stay-at-home orders necessitated by the spread of COVID-19. But even once those orders subside, demand for telehealth services could remain strong as people continue to social distance. Favorable private and public reimbursement coverage and consumer satisfaction with the ease of virtual non-urgent appointments should also encourage future use. Market research company Global Market Insights forecasts that the market for telemedicine will grow at a compound annual growth rate (CAGR) of 19.3% until 2026, when it'll reach a value of more than $175 billion. That's up from $45 billion in 2019.

Potential company and industry growth is good news for investors. Teladoc is an already successful stock that's poised to shoot even higher.

2. Shopify

Shopify rings in at 118 on Robintrack, narrowly missing the Top 100. The Canadian e-commerce company is also experiencing an increase in demand, benefiting from more people staying home and purchasing goods through its platform. Shopify's second-quarter results for the period ending June 30 show sales up an incredible 97% year-over-year to $714.3 million. The sales growth rate was only 47% in the first quarter.

Prior to Q2, Shopify's growth rate was trending down. In 2019, its sales of $1.6 billion were up 47%. The year before that, revenue was $1.1 billion and grew at a rate of 59%. And in 2017, sales of $673 million were up 73% from the previous year.

With that said, 40%-plus growth rates are still impressive. Like telemedicine, the global e-commerce market is rapidly growing. Experts estimate the industry's CAGR will be 11.34% until 2024, eventually hitting a value of more than $6 trillion.

Although Shopify's stock hit all-time highs this year, it could keep climbing as consumers opt to shop online. The challenge for Shopify will be its fight for market share. It faces  competition from big names like AmazonAdobe-owned Magento, and Facebook, where consumers can easily purchase products through Marketplace or its social networking service, Instagram.

Which stock is the better buy today?

Both of these stocks are flying high in 2020 and have outperformed the S&P 500 by wide margins since the start of the coronavirus pandemic:

SHOP Chart

SHOP data by YCharts.

It's unclear why Robinhood investors aren't as excited about these two stocks as they are about other tech and healthcare stocks. But with both companies delivering strong numbers and many growth opportunities ahead, it's not too late for Robinhood investors to jump on board.

If you can only buy one of these stocks today, go with Teladoc. The virtual care provider is in an industry that's not as established as e-commerce. The growth opportunities are much more plentiful and competition is not nearly as fierce. Many of Teladoc's competitors are private and lack the resources necessary to catch up with the telehealth giant. Teladoc is a great option for Robinhood investors who are looking for a surefire growth stock to add to their portfolios.