It's not just merchandise that's on sale today. The holiday shopping season may officially be kicking off on Black Friday, but there are also plenty of stocks that are fetching much lower prices than they were at the start of the year.

Trivago (NASDAQ:TRVG)Qutoutiao (NASDAQ:QTT), and Tilray (NASDAQ:TLRY) have had their share prices cut in half -- at least -- in 2019. These stocks obviously aren't making the cut as some of the market's top stocks of 2019, but the pullback offers an interesting buying opportunity. Let's go over each company and what it did to fall out of favor so far this year. 

Winners of a Trivago hackathon in front of the corporate logo.

Image source: Trivago.

Trivago: Down 57%

Investors have been checking out of online hotel portal Trivago -- instead of checking it out -- this year. Trivago has now posted seven consecutive quarters of year-over-year declines in revenue, even if the 1% dip it posted earlier this month was the kindest of the lot. Trivago also rattled investor confidence this month when co-founder and longtime CEO Rolf Schromgens announced that he would be stepping down, handing the reins to Trivago's CFO.

There's still a lot to like in Trivago. The slowdown in revenue has been partly orchestrated by Trivago -- it's been holding out for higher-quality transactions for the sake of achieving positive earnings. Average revenue per qualified referral is on the rise, and Trivago is helping its bottom line by spending less in generating advertiser leads. Investors don't like the top-line trends, but Trivago is better than its low stock price suggests.

Qutoutiao: Down 53%

Things have gone from feast to famine for the Chinese mobile content aggregator. Qutoutiao went public at $7 last year and was trading in the double digits in the springtime of this year when it went for a secondary offering that diluted both the shares and the enthusiasm, while boosting the stock's float. 

Qutoutiao turned heads as a result of its heady growth, and the 188% increase in revenue it posted in its latest quarter shows that it's still a speed freak. However, Qutoutiao's guidance for the current quarter suggests flat sequential growth. The bottom line is also a mess, and Qutoutiao has posted a larger deficit than analysts were targeting every single quarter over the past year.

The near-term trends aren't kind, but after its hot IPO, Qutoutiao is now trading for less than half of its original price. It's an intriguing play for risk-tolerant investors wanting in on an out-of-favor Chinese growth stock

Tilray: Down 71%

Pot was hot in 2018, but it's been a different story for investors in most marijuana stocks this year. Tilray went public at $17 during the summer of last year, and the Canadian cannabis cultivator skyrocketed to $300 a couple of months later. It's been coming off those highs -- in more ways than one -- ever since. 

The legalization of marijuana for recreational use in Canada late last year and relaxed restrictions stateside have helped prop up the narrative that made Tilray a monster stock last year, but growth has slowed dramatically lately. We're already seeing sequential growth deceleration in adult-use recreational marijuana sales, and Tilray's hemp product sales actually posted a sequential decline in the third quarter.

Tilray is finding outlets for headier growth internationally, but it's coming at the expense of mounting losses. Analysts have been lifting their projections for the amount of red ink that Tilray will be generating in the near term and don't see an actual annual profit until 2022, at the earliest.