Most investors who aren't retiring soon should buy a few small-cap stocks with market values of less than $2 billion. Small-cap stocks are generally riskier and more volatile than mid- and large-cap stocks, but they have more room to run -- which makes them potential multibaggers over the long term.

It can be tough for investors to identify promising small-cap stocks, since many of these smaller companies aren't household names. So today, I'll highlight three speculative small-cap plays that could head much higher: Infinera (NASDAQ:INFN), Impinj (NASDAQ:PI), and Secoo (NASDAQ:SECO).

Stacks of coins behind a stock chart.

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1. Infinera

Infinera's optical systems help internet service providers boost their network capacities without laying down more fiber. Wireline speeds are rapidly rising: Current fiber networks operate at 100G to 200G speeds over long-haul distances, and 400G-600G speeds across shorter distances.

Infinera currently provides 600G solutions to customers, and plans to ramp up its 800G solutions in late 2020 and 2021. That "supercycle" of upgrades should be sparked by the ongoing growth of cloud and streaming services.

Infinera previously generated most of its revenue from long-haul solutions, but it increased its exposure to the shorter-range (metro and data center) markets with its acquisition of Coriant in 2018. The acquisition got off to a rough start last year as the company slashed the initial revenue growth forecasts for the combined company.

However, Infinera generated stable revenue growth over the past year, and its decision to shift production from its Berlin plant to Fabrinet's outsourced plant in Thailand lifted its gross margins. As a result, analysts expect its revenue to rise 10% next year as it narrows its non-GAAP loss back toward breakeven levels.

That growth might seem tepid, but Infinera currently trades at less than one times next year's sales. That low valuation indicates that Infinera's stock could surge significantly higher as more carriers upgrade their networks, and it remains a compelling takeover target for larger networking companies.

2. Impinj

Impinj sells radio frequency identification (RFID) chips for tracking items, along with the systems and software for reading those chips. Demand from brick-and-mortar retailers, which use RFID chips to track inventories and customer trends, has surged in recent years.

An RFID tag.

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Many big retailers, including Walmart and Inditex's Zara, credit RFID chips with streamlining their sprawling businesses. Those success stories convinced other retailers to adopt RFID chips and sparked a positive growth cycle for Impinj. In other words, the more Amazon forces traditional retailers to evolve, the more chips Impinj will likely sell.

Impinj isn't profitable on a GAAP basis due to high stock-based compensation expenses. However, its gross margins are stable, and analysts expect its non-GAAP earnings to quadruple next year with 14% revenue growth.

Impinj's stock is reasonably valued at four times next year's sales, but its low enterprise value of $680 million indicates that it has room to run. It also remains a lucrative takeover target for bigger chipmakers like NXP Semiconductors, which competes against Impinj in the RFID market.

3. Secoo

Secoo is a Chinese e-commerce platform for luxury goods. It went public in late 2017 at $13 per share, but concerns about its decelerating growth, competition from bigger players like Alibaba and JD.com, and China's economic slowdown subsequently cut the stock in half. But if we look at Secoo's core metrics, the stock looks ridiculously undervalued.

Last quarter, Secoo's revenue rose 23% annually, its gross merchandise volume surged 67%, its number of active customers grew 59% to 482,500, and its total number of orders grew 74% to 1.04 million. It's also consistently profitable: Its GAAP net income grew 38% as its non-GAAP net income increased 32%.

Secoo expanded its selection of goods via partnerships with well-known brands like Prada, Stella McCartney, and Stadium Goods, launched a live-streaming channel to directly connect merchants with buyers, and improved its AI-powered recommendations system for shoppers.

Yet Secoo remains nearly invisible to Wall Street analysts. The one analyst that covers Secoo expects its revenue and earnings to surge 37% and 55%, respectively, next year -- which are jaw-dropping growth rates for a stock that trades at 7 times forward earnings. Secoo could struggle to keep pace with bigger platforms, but it seems to have carved out a defensible niche in China's crowded e-commerce market -- and it could be a good speculative buy at these levels.