Weight Watchers International Inc. on Wednesday raised $417.6 million in its initial public offering, in line with increased estimates, in a sign of strong investor appetite for its shares.

The dieting service provider, known all over the world for its weight-loss support groups, sold 17.4 million shares, or a 17 percent stake, at $24 each, underwriter Credit Suisse First Boston said. Earlier on Wednesday, the company increased the estimated price range to between $23 and $25 a share from $21 to $23. 

Weight Watchers' IPO is the biggest offering of new shares on U.S. markets this week, with six companies scheduled to go public. None of the proceeds, however, will end up in the coffers of the Woodbury, New York-based firm, as most of the shares are being sold by Artal Luxemborg SA, a private European investment company that acquired Weight Watchers from H.J. Heinz Co. in September 1999. 

Weight Watchers' stock is expected to start trading on Thursday on the New York Stock Exchange listing under the symbol "WTW''. Other underwriters are Goldman Sachs, Merrill Lynch, Salomon Smith Barney and UBS Warburg. 

The pricing gives Weight Watchers a market capitalization of $2.53 billion, based on 105.4 shares outstanding.