No "stranger danger" here: Unlike Craigslist or eBay, the Facebook group is open only to classmates, recent graduates, local friends, or younger brothers.
"That's part of the attraction; it's easy to make the deal," said Mac Melman, a senior at Lower Merion. "You can just meet in the hallway outside math class. You don't have to trust random people."
It started more than a year ago when sophomore Miles Keller made the mistake of asking whether anyone wanted to sell him headphones on a similar Facebook group for girls.
"The girls freaked, telling me that the group was only for girls and only for clothes," said Keller. "Then they booted me out. So I started one for guys."
The group for guys caught on almost immediately, as word spread that there was now a way to make some bucks from all those old video games and sneakers. The items listed for sale change frequently, often several times a day, as the 440 members can attest.
Technologically agile and fast on the keyboard, the teens close deals quickly. If you snooze (or you're actually doing homework on the computer, not Facebook), you lose. A post asking for "nice neckties, preferable for a tall guy," was answered almost immediately by a classmate who wanted to know, "funny or classy? I got all."
Only a teenage boy can have a video game emergency, as indicated by the post that pleaded "need Halo 4 now pleeeeaase." Luckily, two minutes later, a classmate responded with "I gotchu." The deal was sealed in minutes with the message: "txt me meet @ lunch."
In the group, haggling is crucial and the guys are not shy about outbidding a friend for a coveted item. "There is definitely a lot of competition to outbid other guys," Keller says. "It can get annoying when I'm trying to get something and I'm ready to meet the seller and someone else jumps in and posts 'I'll give you $5 more,' and I lose the item."
It's no wonder that the online group, with opportunities to haggle, insult and banter, appeals to teen males, says Bev Cutler, assistant director of counseling and psychological services at Saint Joseph's University and a private practitioner in Bala Cynwyd.
Shopping together in malls may offer teen girls social connectivity, but boys are more likely to bond through such organized activities as video games, or through such activities as sports.
"If you add to the mix the unsupervised back-and-forth exchanges on social media sites that allow immature humor and spontaneous social connections to flourish, it makes perfect sense why teenage boys are creating and using groups like this one," Cutler says.
Friendships have been formed, too. Narliotis met a fellow skateboarder, a student at nearby Harriton High School, through the group. "I sold him an old long board, and after we made the exchange, I went skating with him that day," he recalled. "That is one good thing about the group - we're all kids from the neighborhood. Even if they go to a different school, chances are they live close."
The unpredictability of the items up for sale is also part of the appeal. In early December, a pet snake was offered up including a heat lamp, log and the promise that "he helps attract the girls." A father's BMW, tastefully pictured on the River Drive, and a pair of (used) pajamas were also once posted. The car never reached a minimum acceptable bid and the pajamas just elicited a bunch of "ewww, gross" comments.
When an objectionable item is listed, it's often met with a flurry of "Really, dude?" and "You're kidding, right?" posts. One regular reported that someone once listed 50 basketball jerseys that may or may not have fallen off the back of a truck. But it seems that peer approval is often enough to police the marketplace.
"I'm really into sneakers and I can tell a knock-off right away," Melman explains confidently. "Whenever someone posts a fake sneaker, I have to comment and call him out because kids will get ripped off."
Unlike a standard auction, sellers often underprice in an effort to seal a deal - the competition is that fierce. For instance, $100 headphones have been known to go for $40. One user said, "Let's face it, in this neighborhood, everyone has everything - and they want to sell it to get something else."
The group also satisfies the first necessary steps of the teen years: breaking away from parents and establishing independence.
Of course, parents will likely want to know something about their transactions.
Robin Wilen caught on when her 17-year-old son, Ari, came home wearing a new pair of sneakers.
"Ari told me he bought them online, but they didn't come in the mail like other things," she said. Wilen says she was reassured to learn that the group was all local boys, but she has some mixed feelings: She thinks her kid has a sneaker obsession. Still, Ari earns his own money, "and it's not like he brings home new property every day. And if they want to trade, let's face it - it's their stuff."
Letting the deal go down without parental supervision is vital to the learning experience, says parenting expert Barbara Greenberg, a clinical psychologist known as the Teen Doctor for Psychology Today. She was impressed by the entrepreneurship and ingenuity of the members.
"When your son comes home with a new shirt, it's OK to ask where he got it, but that doesn't mean interfering in the process. That's helicopter parenting," she said. "The back-and-forth bantering and exchanges sound like a great way for the boys to learn life lessons without big consequences." Like the life lesson of paying too much for a sweatshirt.
Anticipating the odds that Christmas might also disappoint, Melman posted to the group in December reminding users they could unload any unwanted gifts. He's looking forward to a flurry of activity as guys try to trade that sweater from Grandma for something truly useful - like a snake.