Stocks have had a good run through the first six months of the year, but they haven't all been winners. Some investments have been stuck on the sidelines, and that includes dozens of stocks that have actually plummeted by more than 50% in the first half of 2019.

Weight Watchers (NASDAQ:WW), GameStop (NYSE:GME), and (NASDAQ:STMP) are some of the unfortunate stocks that have been cut in half -- and then some -- over the past six months. Let's go over what each company did to fall out of favor so far this year. 

The Weight Watchers online platform for digital subscribers.

Image source: Weight Watchers.

Weight Watchers: Down 56%

You can go from feast to famine, and that's how one of the market's hottest stocks two years ago has been losing a ton of weight in 2019. The provider of weight management solutions took off in late 2016 after Oprah Winfrey acquired a small stake in the stock and became its official spokeswoman. Aspiring pound shavers followed Winfrey into Weight Watchers, and investors followed suit. The stock soared 783% from the start of 2017 through the midpoint of 2018, but it's been backpedaling ever since. 

Winfrey's arrival was good for six straight quarters of double-digit percentage growth in revenue, but that momentum is stalling. Business is going the wrong way now, and that includes a double-digit percentage decline in revenue last time out. Weight Watchers still has 4.6 million subscribers, just as it did a year earlier, but the dynamic of those members is changing for the worse. More than two-thirds of Weight Watchers customers are now digital subscribers, a challenge because they pay less than half of what in-store support members shell out and spend less on the branded meals. Weight Watchers is now trying to position itself as a wellness brand to capture more than just the weight conscious, but that's not going to be an easy sell.   

GameStop: Down 55%

GameStop is living on borrowed time. Cartridge- and disc-based gaming is fading, as die-hard gamers turn to digital distribution and casual players gravitate to cheaper mobile diversions. GameStop is still selling the hardware necessary to kick off the gaming experience. But the slow fade of its higher margin software and -- more important -- its pre-owned games business is hurting the chain.

Income investors replaced growth investors a few years ago given the stock's chunky yield, which was closing in on 20% earlier this year. But the dividend chasers followed growth investors out the door when GameStop decided to eliminate its payouts last month. The reeling retailer had kept the distributions coming as it tried to smoke out a potential suitor, but that avenue hit a dead end earlier this year when it announced that it was no longer exploring strategic alternatives. It's not "game over" here given the chain's current profitability, but it's hard to see GameStop ever clawing back its relevance. Down 71%

Putting all of your eggs -- or in this case, stamps -- in one basket can be a dangerous game. The provider of online postage and shipping solutions took a hit after announcing that its exclusive partnership with the U.S. Postal Service would be ending. tried to position the deal's termination as a way to strike up partnerships with other carriers, but investors saw the end of the cash cow. 

Its stock has lost at least half of its value in back-to-back quarters, and the former market darling's guidance paints an ugly near-term picture. After eight years of double-digit revenue growth, is eyeing a decline on the top line with adjusted earnings falling by nearly as much as this year's 71% stock plunge. It's mail pattern baldness. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.