NEW YORK (AP)--Shake Shack served up fourth-quarter results and a sales outlook that disappointed investors hungry for more rapid growth at the trendy hamburger chain.

The combination triggered an 8 percent decline in Shake Shack's stock price in extended trading Monday after the numbers came out.

Both Shake Shack's earnings and revenue topped analyst estimates, but that still wasn't enough to overshadow a conservative forecast for this year.

The New York company expects its 2016 revenue to range from $237 million to $242 million, within the $240 million projected by analysts surveyed by FactSet.

But investors appeared to be fixating on Shake Shack's expectation that sales will only increase by 2.5 percent to 3 percent at its outlets that have been open for at least two years. That's a dramatic slowdown from the 13 percent increase in so called "same-Shack" sales posted last year.

Shake Shack's stock sank $3.38 to $38.85 in extended trading. Boosted by the popularity of its burgers and fries, Shake Shack's stock soared to as high as $96.75 last May after pricing at $21 in a hotly anticipated initial public offering at the outset of 2015. The stock has backtracked as more investors realized Shake Shack's earnings might not be as delectable as its burgers.

The company earned $1.2 million, or 7 cents per share, during the final three months of last year, swinging from a loss of $1.4 million, or 5 cents per share, during the same period in 2014.

If not for certain items, Shake Shack Inc. said it would have made 8 cents per share--a penny above the predictions of analysts polled by Zacks Investment Research.

The company posted fourth-quarter revenue of $51.1 million, a 47 percent increase from $34.8 million in the prior year. Analysts had anticipated revenue of $50.6 million, according to Zacks.

For the full year, the company reported a loss of $8.8 million, or 65 cents per share, after eking out a $2.1 million profit in 2014.

Shake Shack ended the year with 84 locations and plans to open at least 13 more outlets this year in the U.S., including new markets in Los Angeles, Phoenix and Dallas.

--Associated Press