From adulterous middle-aged marrieds to millennials who say only freaks chat up people in bars, millions of Americans are finding love online as technology corners the market in romance.

New York has a reputation as a party capital of the world, where sex is free and easy and unmarried adults outnumber their married counterparts.

Glued to smartphones at every waking moment, New Yorkers shop online for everything from jobs to food. So why not love?

Promises of lasting happiness, a kinky affair or a one-night stand -- all at the click of a button -- are dangled before lonely hearts who sign onto a dazzling array of dating sites.

Andrea Morales, a 25-year-old graduate student from Costa Rica, used to think Internet dating was a bolt-hole for the desperate. Then she moved to New York.

"A lot of people I met here started telling me it's super normal," Morales says. "At first I felt weird about it... but it's really hard to meet new people apart from your friends."

She signed up to Tinder and OkCupid, and found herself going on three dates a week. She met her last girlfriend online. The couple dated for seven months before breaking up.

"I didn't have any really horrible experiences," says Morales. "But most of my straight friends had horrible stories, because there are creepy men out there."

Online dating is all the more attractive in a city where friendship groups are tight, relationships at work can be perilous and where dalliances in bars are viewed with suspicion or quickly forgotten.

About 31 percent of people now meet their last love interest online, anthropologist Helen Fisher told CNN.

Match.com, which claims to be the world's largest dating site, says it has created more than 10 million relationships in the United States in 20 years.

But there are pitfalls: hackers breached the online adultery website Ashley Madison -- which claims millions of users worldwide -- and threatened to expose data on users.

- 'I'll just swipe again' -

"Technology is not changing love. Technology is changing how we court," Fisher told CNN. "It can never change love. Love is an ancient brain system."

Morales says she has spent up to 20 minutes at a time "swiping" through photographs of prospective dates on Tinder.

"In New York, there's always someone else. It's just full of young, fairly educated, fun people so there's always this idea of whatever. I'll just swipe again," she says.

"I feel people are more disposable."

Tinder was set up in 2012 and claims to create 26 million matches around the world every day.

The app puts people in touch who "swipe right" on photos of each other -- indicating potential attraction.

"Tinder has revolutionized the way that people meet," a company spokesperson trumpeted. "'Swipe left' and 'swipe right' have become a part of the cultural vernacular."

For younger New Yorkers, Tinder has become a way of life -- or at least a crutch to get through lean times in love.

One 24-year-old woman, who works as a designer and asked not to be named, said she had a tight circle of friends and was younger than her colleagues, so the Internet was the only place to meet partners.

"It's creepy for men to hit on you in a bar, or in the street or in a train," she said. "Most girls have that little edge that something bad will happen, that they (the men) are freaks.

"It weirds me out," she says. "I've never met up with someone I haven't talked to for a few days."

But an online facade can quickly unravel in person.

"One guy I thought was cool and normal told me 'I'm bisexual and I'm probably going to jail because of all these drugs I sold.' And I was like, 'I don't actually like you very much,'" she says.

- Happy ever after -

Sites provide access to more potential partners, but browsing and comparing can reduce willingness to commit to one person, cautions an article in the journal Psychological Science.

There is "little evidence" that "algorithms can predict whether people are good matches or will have chemistry with one another."

But curriculum director Emily Helfgot, 42, and librarian Robert Weinstein, 44, are the lucky ones. They met online in 2012. Three years later, they are married.

Helfgot says she used dating sites "on and off probably for three years" before meeting Weinstein. He had just gone back online after a previous relationship fell apart.

"What I learned was exchange a couple of emails, and they should be meaty, you should be getting something out of them and then you should meet as soon as possible," she said.

They happened to live in the same neighborhood and they hung out at the same places. They wondered whether they would have met in real life and whether they would have liked each other.

Weinstein confesses to "a bit of a stigma" about how they met but says the embarrassment "went out very quickly".

"For all the pitfalls, annoyances and tumult of online dating, I'm so glad I did it!" said Helfgot.