"Respect for the girls disarms them—they're not used to it. Be funny and humorous. And power tip No. 3? Don't lock in too early on any one girl."

It's a sweat-through-your-statement-shirt Saturday afternoon in Medellín, Colombia—the former murder capital of the world. Dave, a stocky ex-nightclub manager from Liverpool, England, is preaching to a crowded bus of single men. They've traveled from Europe, Australia, and the United States to meet single women, maybe even marry them. Dave is the dating coach at AmoLatina, a subsidiary of Anastasia International, an international online dating portal that includes AnastasiaDate.com, AmoLatina.com, AsianBeauties.com, and AfricaBeauties.com. Once a romance-tour client himself, Dave's all lovable swagger and rogue British charm. It's easy to see why the men around me have bought into him and his power tips.

We're en route to a dating party organized by AmoLatina. Our minibus peels off a busy highway and into the parking lot next to an unassuming club called Dulce Jesús Mio. We head inside and take in the Latin-village decor that's oddly punctuated with wall-to-wall Christmas lights and large, grinning porcelain pigs. It looks like the kind of place that celebrates New Year's every night. (And every night at midnight, it does.)

The music starts. Reggaeton—a fusion of Latin hip-hop, dancehall, and salsa—echoes through Medellín no matter where you go. Its pulse is the hypnotic "dem bow" beat: a mesmerizing pattern that never ceases.

A taxi lets locals out near the club called Dulce Jesús Mio.

Women begin arriving in groups of three and four, spilling out of bright yellow taxis. We see glimpses of halter tops and jeans, outfits keenly hugging voluptuous figures. The youngest, smiles lined with braces, are in their early twenties. The oldest look to be in their mid-forties and strut toward the club with less giggle, more purpose. Photographers have been hired to capture the women as they enter the club, blinding flashes lighting up their faces in front of an AmoLatina sponsor board, which reads: bringing the world together.

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The phenomenal growth of online dating over the past two decades shows no signs of slowing. It has skyrocketed from a curiosity in the late 1990s to a $2 billion powerhouse in 2011. Anastasia International, most famous for arranging meetings with Russian women, was founded in 1993 and has more than 240 employees, working in offices from Maine to Moscow to Medillín. They run regional websites in Eastern Europe, South America, Africa, and Asia. The company boasts that nearly one in five of its customers ends up either married or in a "lasting relationship" after attending one of its Eastern European romance tours. It also claims that the number of men joining has more than quadrupled since 2005—and that sign-ups by Russian, Ukrainian, and Latin American women have tripled.

Here's how it works on AmoLatina: Select one of 27 countries (the parent company works with 113 nations in total) from a drop-down menu, then identify the traits you would like in your ideal partner: age, height, weight, hair color, eye color, and even English-speaking skills (which range from "fluent" to "beginner"). If a profile piques your curiosity, you pay for an online introduction. Fees range, based on whether you want to send translated messages to the women, have roses delivered to their doorstep, or go on a guided tour in their hometown to meet them. Of course, you can always forgo formalities and book a tour without doing any preliminary browsing. Most customers travel to meet as many women as possible in one particular city.

The participants on this trip paid $1,595 for a package that includes accommodations at a four-star hotel (the Hotel Dann Carlton Belfort Medellín), in-house translators, and access to hordes of women at two "socials." The central office of the romance tour is housed in a spacious hotel hospitality suite, with open windows overlooking downtown. This is where clients set up dates with women they've spotted on the website or at a social.

Downtown Medellín, Colombia (pictured). What was once the murder capital of the world is now an international matchmaking destination.

The guys on my trip range from 26 to sixty-something. Aggie, a hulking, cheery real-estate executive from Los Angeles, appears to be about 30. He's already befriended Mark, a six-foot-five undertaker from Boston. They make for a boisterous duo. Steve, from Omaha, is a grandfather and a widower. Joe, a middle-aged divorcé from Boston, works at one of the world's biggest tech companies and resembles Jon Lovitz—right down to the billowy polo he's wearing. Joe is brash and self-deprecating but softens when he talks about meeting a potential partner. Many of the men on tour in Medellín have experienced heartbreak, betrayal, and loneliness. Some pine for a wife and children. A minority are "players" who expect a tangible return on their investment. So says Dave, who confesses to taking a group of men to a strip club—which doubled as a brothel—in Bogotá a week earlier.