In recent weeks, the postings on Craigslist have taken on a desperate tone: "Looking for two tickets for . . . Jan 12th. Willing to negotiate price."

"In search of 1 ticket. . . . Price negotiable!"

"Forgot to purchase, and they are now sold out. Please email or text if have tickets."

These hot tickets were for, of all places, the Franklin Institute - more specifically, Science After Hours, the museum's monthly, no-kids-allowed science rave.

More than 2,600 people bought tickets for the Tuesday-night event, a speakeasy-theme gathering focused on the science of booze and bootlegging.

It's scientific proof that extended hours, a 21-and-older environment, special programing, and a cash bar can be a potent formula for attracting millennials who might not otherwise consider visiting the museum.

So it's no wonder that institutions around the city are increasingly looking to such events to do what exhibitions may not: get a new generation of young people buzzing (and tweeting and Instagraming) about museums.

"All science museums have struggled with that 21-to-40-year-old group," said Frederic Bertley, the Franklin Institute's senior vice president of science and education. "We wanted to figure out: How can we cleverly get them in the door? But we don't want to sell out the soul of the Franklin Institute and what it's all about, which is science learning and hands-on, really cool experiences."

Over the last decade, institutions like the California Academy of Science in San Francisco and the Museum of Modern Art PS1 offshoot in Queens have become known among twentysomethings as much for their raucous dance parties as for their exhibits.

In the last few years, more Philadelphia museums have explored such possibilities.

The Philadelphia Museum of Art added a Wednesday-evening pay-what-you-wish series with yoga, art-making, and games, as well as gallery access. The Academy of Natural Sciences has hosted Mystery Science Theater 3000-inspired movie nights and adults-only sleepovers with booze. And the Pennsylvania Academy of the Fine Arts last year launched its own Wednesday-night offering, Art in Process, a series of lectures, performances, and activities.

"Many museums are at a point where they see their core audience as a slightly older, baby-boomer audience and are interested in finding ways to continue to be relevant," said Emily Schreiner, curator of education and public programs at the Art Museum. "We know millennials tend to use the museum in a social way."

Events like Wednesdays at the Art Museum - a program in its pilot phase - aim to change perceptions of what a museum can be.

"Not everyone thinks that museums are exciting, but they think hanging out with their friends is," said Kate Quinn, exhibitions and public programs director at the University of Pennsylvania Museum of Archaeology and Anthropology. "So we need to create a stronger social environment, so people can think about us differently and about museums differently. They can be fun places."

She wants young professionals to consider the museum their "third place" - a concept described by sociologists as a social and inclusive place that's neither home nor work.

To that end, she has expanded the P.M.@Penn Museum outdoor summer program to include year-round evening events. Past offerings have included offbeat gallery tours, drag shows, concerts, and hands-on activities, in addition to drinks and music. The next one, Feb. 17, coincides with the exhibition "Sex: A History in 30 Objects" and includes brief lectures, a burlesque show, and chocolate-making.

And, she said, the museum is rolling out a new happy-hour series called Mummies and Martinis.

The potential benefits for museums are numerous.

There's the initial revenue bump (Science After Hours, in its first full year in 2015, brought in more than $200,000). Then there's the hope that these young people might return - on their own, with friends, or with their own children a few years down the road.

Besides, young visitors may be at the age where they're planning weddings and office parties. Some have followed up after evening events to inquire about rentals.

The challenge in all this, though, is staying on mission, said the Franklin Institute's Bertley. Science After Hours includes about 20 stations showcasing specimens or scientific phenomena. That helps set a tone that it's something other than a party.

"A lot of museums around the country have gone the party route. But that's a scene that requires bouncers and how they tear up the museum on a given night. They bring in revenue," he said, "but it's a different model than ours."

He said Science After Hours was still, above all, about science literacy.

Even without the bouncers, it has attracted devoted fans like Andrea Anastasi, 28, a lawyer who lives in South Philadelphia.

She came across the Franklin Institute's Science After Hours on Facebook.

"I kind of became a big fan," she said. "I was an English major in undergrad, but they make the science super-accessible, and it's very interactive. You do things that you wouldn't normally get to do. Last time, I held a human brain in my hands."

She attends every month if she can and recruits friends to join her. Recently, she started volunteering at the museum.

"The life of a 28-year-old isn't always that exciting," she said. "But at least once a month, if my schedule permits, I have something I know will be uplifting and educational and inspiring to look forward to."


Science After Hours: "Seven Deadly Sins"
7-10 p.m. Feb. 9 at the Franklin Institute.

P.M.@Penn Museum: "What's Love Got to Do With It?"
6 p.m. Feb. 17 at the University of Pennsylvania Museum of Archaeology and Anthropology
$20 includes one drink

"Mummies and Martinis"
6 p.m. March 3 at Penn Museum
$9 includes one drink

Wednesday Nights
5:30-8 p.m. weekly, with a special Museum RX medical-theme evening
Jan. 27, at the Philadelphia Museum of Art
Pay what you wish

Overnight for Adults
6:30 p.m. April 9 to 9 a.m. April 10 at the Academy of Natural Sciences
$190 includes dinner, breakfast, drinks, activities, and next-day museum admission