(Reuters) - Shares of Zoe's Kitchen Inc <ZOES.N>, a casual dining chain, rose as much as 73 percent in their market debut on Friday, underscoring strong investor appetite for U.S. restaurant-related stocks.

Zoe's debut comes on the heels of a successful listing by food delivery service GrubHub Inc <GRUB.N>, whose shares jumped as much as 57 percent in their trading debut a week ago.

This week has been the been the busiest for U.S. initial public offerings since 2007.

More than a dozen companies were lined up to go public this week but four, including Lombard Medical and Stalwart Tankers, failed to price on Thursday.

About $16 billion has been raised in U.S. IPOs so far this year, making it the best period in more than a decade.

Zoe's Kitchen raised about $87.5 million after its IPO of 5.83 million shares was priced at $15, the upper-end of the expected price range.

Zoe's shares opened at $25.65 and touched a high of $25.90 on the New York Stock Exchange, valuing the company at more than $475 million.

Private equity firm Brentwood Associates' stake in the company has dropped to 45.4 percent from about 70 percent.

Founded in 1995 by Zoe and Marcus Cassimus in Alabama, the restaurant chain offers Mediterranean-style cuisine with southern staples inspired by family recipes.

The company, which has a 111 restaurants, is part of the growing fast-casual category.

A fast-casual restaurant does not offer full table service but serves healthier food than a fast food restaurant.

The fast-casual business generated $31 billion in sales in 2012 and is projected to grow to $50 billion by 2017, according to consulting firm Technomic.

Zoe's revenue rose 46 percent to $116.4 million in 2013, but its net loss widened to $3.7 million from $253,000.

Jefferies & Co and Piper Jaffray were lead underwriters to the offering.

(Reporting By Neha Dimri in Bangalore; Editing by Savio D'Souza)