Image source: Weight Watchers.

Marketing campaigns don't typically trigger big stock moves, but it does if you're Weight Watchers (NASDAQ:WW) and your new ad's star is shareholder Oprah Winfrey. Shares of the weight-management specialist soared 17.6% last week, after the new ad finds Winfrey revealing that she has lost more than 40 pounds on Weight Watchers. 

The "Live Fully" campaign is timed to coincide with the end of the year, when losing weight becomes a popular New Year's resolution. This is an important time for gym operators, car dealers, and weight-loss centers. Weight Watchers has had Winfrey on its side since she acquired a 10% stake in the company 14 months ago. She's making her own luck as a stakeholder by becoming a vocal advocate for the weight-management platform.

The campaign kicked off on Thursday with a pair of TV ads, both starring Winfrey detailing her favorable experiences with Weight Watchers' Beyond the Scale program. The campaign tackles the positive angles of both the food and community at Weight Watchers and the benefits of attaining good health.

"I struggle no more," she says in one of the spots. "I've eaten everything I love. I've never felt deprived."

"I would say to anybody who's thinking of joining Weight Watchers, take the leap and get about the business of enjoying a full and fantastic life," she concludes.

Stepping on the one scale that matters for investors

Unfortunately for Weight Watchers shareholders, it's not just Winfrey losing some serious weight. The stock has shed 47% of its value this year, even with last week's nearly 18% gain.  

The stock is still trading higher since Winfrey's arrival in October of last year, a testament to the big initial pop that Winfrey's association helped inspire. Winfrey is a media mogul, but her ups and downs with weight management made her a natural spokesperson for an iconic weight-loss brand in a state of disarray.

The stock improved before the fundamentals. Its active subscriber base declined in 2015. Growth in its net revenue and operating profit have been flattish through the first nine months of 2016. Winfrey's impact has been more assumed than realized, and that explains why the stock hasn't lived up to the initial hype. 

Weight Watchers is still in a good place. Winfrey's heading up a few campaigns over the past year, and sooner or later one's going to resonate with her huge fan base. Along the way, the stock's trading at a reasonable 12 times the midpoint of its earnings guidance for all of 2016. Weight Watchers stock has a long way to go to get back to where it was, but with management cutting costs and another promising campaign rolling out, the future looks brighter for investors in 2017 than it has been in 2016.