Investors are giving Oprah a round of stock-buying applause.

(Bloomberg) — Weight Watchers International Inc. (NYSE:WTW) shares surged almost 30 percent over the past two days after Oprah Winfrey debuted a campaign endorsing the weight-loss program.

The celebrity and media mogul posted a video to her Twitter account about using Weight Watchers to lose weight. “Are you ready?” she asks in the clip. “Let’s do this together.”

The video renewed investor optimism that Winfrey can help turn around the long-struggling company. Winfrey, 61, announced her partnership with Weight Watchers in October, saying she would buy 10 percent of the stock and join the board. The plan is for her to share her experiences using the program.

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The longtime talk-show host has sparked a huge rally for the stock, sending it up more than threefold since she began backing the company. The value of her 10 percent stake, which would have been worth about $43 million before she joined Weight Watchers, is now valued at almost $150 million.

Weight Watchers climbed as much as 23 percent to $23.78 on Wednesday, its biggest intraday jump since Nov. 6. That follows a 7 percent gain on Tuesday, when Winfrey posted the video.

—With assistance from Janet Freund.

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