LOS ANGELES — Forever 21 Inc. built a retail empire by selling the latest fashion trends, but when it comes to running its own business, the Los Angeles company isn’t following the crowd.

During the recession, when Mervyns and other chains were going bankrupt and shutting stores, Forever 21 snatched them up.

At a time when competitors, worried about taking risks in a down economy, focused on basics like T-shirts and jeans, Forever 21 continued to churn out fresh and trendy merchandise.

Now as traditional big-box retailers such as Walmart, Target and Kohl’s are opening smaller retail locations, Forever 21 is aggressively super-sizing its stores.

Its latest megastore opened this month in Los Angeles, when the family-owned company consolidated three stores into a new 45,000-square-foot space, more than doubling its presence in the Beverly Center shopping mall.

The retailer also took over an 86,000-square-foot former Mervyns in Cerritos, Calif., last year and a 91,000-square-foot location in Times Square in New York. Its new Las Vegas flagship is 127,000 square feet, about the size of an average Target, and in September, it will open a store in Mission Viejo, Calif., in a building previously occupied by Saks. Its biggest store, at 150,000 square feet, opened last month at a shuttered Gottschalks location in Fresno, Calif.

With spaces that large, Forever 21 is moving into unknown territory for a cheap-chic retailer: No longer relegated to the cluttered-and-cramped feel of many of its smaller stores, the company is bringing its rapidly changing merchandise into huge spaces typically associated with department stores.

And with a growing lineup of categories — maternity, plus sizes, cosmetics, children’s, swimwear and shoes among them — all sold at bargain-basement prices, retail analysts say the retailer is shaking up and redefining the traditional mall anchor concept.

But is bigger better? Retail experts aren’t sure.

“Do I normally advise my clients to expand? No. But in times like this, if you have good reason to expand, then I think you take advantage,” said Marshal Cohen, chief industry analyst at NPD Group. But “they’ve got to be careful that they don’t get too big.”

Forever 21 is “almost taking a mini, hipper department-store approach,” said Christine Chen, a retail analyst at Needham & Co.

“The question really is: How sustainable is what they’re doing?” she said. “They have defied odds and skepticism, but going forward they have all these really large locations. As they go into more and more markets and become more ubiquitous, does the coolness factor at some point in time go away?”

The bigger stores have generated a lot of buzz, but they’ve also translated into increased business, President Alex Ok said. With more room for varied styles, shoppers are spending more time and money in the larger stores; the company is also seeing a wider clientele.

“People used to say we were a two-generation store. Now we’re a three-generation store,” Ok said.

The privately held company, which is headquartered just south of downtown LA, has 481 stores in eight countries — 100 of them in California — and more than 33,000 employees. Besides opening giant stores, it is working on an aggressive expansion in Europe.

In 2009, the most recent year that the company released sales figures, it reported revenue of $2.3 billion. This year, it is projecting revenue of more than $3 billion.