SANTA CRUZ, CALIFORNIA• Jason Aaron Baca is good-looking, not handsome like the Ryans (Gosling and Reynolds) or rugged like Daniel Craig, who is fetching in a tailored Tom Ford suit. But when Baca, 42, slipped on a pair of dark aviator glasses recently, he looked remarkably like Tom Cruise in Top Gun (1986).

He was dressed for work in a khaki military jumpsuit. And even though it was barely noon, he had already stopped by the gym to make sure his biceps and legs looked combat-strong. His assignment: To be a military helicopter pilot saved in a crash by a female rescuer with whom he once had a torrid affair. Reunited, their passions have flared.

Baca is a cover model for romance novels. He has been on nearly 500 book covers by his own account - one of scores of men like him vying to be heroic heart- throbs. Not since the flaxen-haired Fabio Lanzoni dominated drugstore book racks in the 1980s and 1990s, with his lion's mane and bulging biceps, have cover models been in such demand.

"Look at me like you are really mad at me," cooed Portia Shao, his photographer that day. "Show me your good side."

After a few more clicks of the shutter, he and Shao paused to examine his work on a 2-by-4-foot television screen.

"It looks good because it has everything," Baca said. The smouldering gaze. A glimpse of his six-pack abs. He had even thrust his pelvis forward, a trick he learnt to make his stomach appear flatter and ensure the women looked, well, you know, there.

Romance writers and publishers, as it happens, are among publishing's most innovative participants. They were early to digital serialisation. Book sellers, too, now crowd-source ideas to find fresh writers. And if you want to explore a virtual relationship, you can try a romance-novel app.

How hot are romance novels? Overall, annual sales totalled US$1.08 billion in 2013, according to the Romance Writers of America, which tracks sales. And their popularity is expected to grow.

Last year, Scribd, an e-book subscription service, sharply reduced the number of romance and erotica novels it offered because it could not afford to keep up with readers' appetites. (Scribd pays publishers every time a book is read and loses money if a book is too popular.)

Despite the perception that blockbusters such as Fifty Shades Of Grey drive sales, self-publishing has proved a boon for this particular genre. E-books make up nearly 40 per cent of all purchases, according to the writers' group. And there are categories for every reader's taste, among them, adventure, Christian, multicultural, LGBT and paranormal.

Enter Baca. Authors and publishers require a revolving door of new faces, which, while hard to estimate, tally somewhere in the hundreds each year.

"I never thought I would say this," said Ms Liz Pelletier, chief executive of the romance novel company Entangled Publishing. "But I am so tired of looking at men's abs. I don't know if these ones are sexier than those other ones."

"It used to be that everyone wanted Fabio," she added. Today, though, individualism prevails. "Readers don't want every book to have the same face."

It was January and Ms Pelletier was bemoaning how tough the search for a perfect cover model can be. Entangled Publishing is five years old, one of the newer entrants to an industry whose identity is synonymous with Harlequin, the Canadian publisher, which in the early 1950s started publishing chaste romance stories set in hospitals and medical offices.

Harlequin reached its zenith in the United States in the 1970s when reader appetite shifted to more sexually explicit fare, known as "bodice rippers" or "sweet savages".

Sexy still sells. At Brazen, Entangled's more risque fiction line, Ms Pelletier said book covers with male models sold three times more than with a woman alone. And for new authors in particular, "the cover is really critical", said Ms Dianne Moggy, vice-president for romance fiction at Harlequin.

Unlike the Fabio era, when covers were painted by hand, today they are more assembly line than art. Consider Daemon Black, a space alien with dark curls and emerald- green eyes who is the hero of Entangled's Lux series, written by The New York Times best-selling author Jennifer L. Armentrout.

In 2011, Pepe Toth saw a photograph of himself and his then-model girlfriend, Sztella Tziotziosz, on the cover of Obsidian, the first in the Lux series published that December.

Toth, 26, then living in his native Hungary, had been transformed into Daemon Black without his knowledge. "I thought, what kind of book is this?" he said in a recent interview.

Toth, a professional soccer player, learnt that Armentrout had used a stock photo taken from a shoot he and his girlfriend had done three years earlier in Budapest. So, he e-mailed the author. "I'm the guy on your book," he said he wrote. Armentrout invited him to visit the US.

In June 2012, Toth and his girlfriend flew to Atlanta after Entangled organised #DaemonInvasion, a promotion for Lux fans.

"When I landed, I said to Jennifer, 'I don't know you,'" he recalled. "She said, 'But you have a lot of fans.'"

He and his girlfriend filmed trailers to promote the series and accompanied the writer on a book tour. At the FoxTale Book Shoppe in Woodstock, Georgia, one afternoon, Toth found himself surrounded by almost 50 cheering women.

"People called out to me, 'Oh, Daemon is here!'" he said. One woman started crying. "She didn't want to step up to have a book signed because she was so happy," he said. "It was really weird."

Today, he posts book signings on his twitter account, @Daemon- Black and he reads excerpts on YouTube. And when Entangled considered dropping him from the cover after he split up with his girlfriend, Ms Pelletier said: "There was a revolt from readers." Now Toth is featured alone.

Few romance models, if any, make enough money to eke out a living. Baca, for example, works at the Housing Authority of the County of Santa Clara, California, as a customer-service clerk.

And although he has an agent, he said he earned only US$20,000 in his best year. This, despite the fact that he is a tireless self-promoter who fancies himself the next Fabio. Industry executives say it will be difficult to topple the king.

"Nobody did it better than Fabio," said Ms Allison Kelley, executive director of the romance writers' group. "He really did create the brand."

Baca's dream had always been to be on the cover of Playgirl. In his 2004 book, Journey Of A Male Model, he wrote that a Seattle photographer once shot him nude for a possible Playgirl spread. Instead, those photos landed on the cover of gay men's magazines under a pseudonym.

Baca said he did not know then to secure the rights to his photographs. (For the curious, he finally made Playgirl in 2004.) And he maintains he does not do it for the money. Instead, cover modelling gives him a taste of fame in an otherwise low-key life. "Nobody else knows this secret life," he said. "They just think I'm Jason."

NEW YORK TIMES