Weight Watchers, which also announced plans to "resize," said it expects to earn $1.30 to $1.60 per share in 2014.

Analysts on average expected earnings of $2.78 per share, according to Thomson Reuters I/B/E/S.

The company said it would finalize plans to reorganize its business in the current quarter. The costs associated with the plan are not included in the earnings forecast, it said.

"2014 will be a very challenging year," Chief Executive Jim Chambers said in a statement on Thursday.

Wedbush Securities analyst Kurt Frederick described the outlook "shockingly bad."

"(Membership) trends have been bad, trends are bad now. Expenses are also not adjusted yet to reflect the declining business," he added.

The company, which faces competition from diet apps and calorie-counting gadgets, said membership paid weeks dropped 8.5 percent in the fourth quarter.

Weight Watchers, which also offers a line of diet foods, reported a 47 percent fall in profit.

The company suspended its dividend in the previous quarter.

In aftermarket trading Thursday, Weight Watchers shares were down $5.98 at $24.60. The shares rose 3 percent to close at $30.58 on the New York Stock Exchange. As of Wednesday's close, the stock was trading at a forward price-to-earnings multiple of 10.78, compared with the peer group average of 18.27.

Weight Watchers rival Nutrisystem trades at a multiple of 20.94.