LOS ANGELES—Snap, Inc. the parent company of the Snapchat app, has a loyal base of nearly 160 million visitors daily, mostly teens and young adults.

So when it went public, who snapped up Snap stock?

Young investors.

Ryan Eshaghi, an 18-year-old freshman at the University of California, Irvine, said he became "addicted" to the app when he was in eighth grade. "It defined the way teens and young adults communicate with one another," he says.

Eshaghi says he bought his 20 shares for the long term, financed by his part-time job helping high school students with college applications. "I see the company growing a lot," he says.

"There’s a lot of upside in Snapchat going forward and I wanted to partake in its IPO,” said Will Jamieson, 23, who works in marketing in Charleston, South Carolina. He also owns Tesla shares.

After two days of euphoria, however, these early Snap investors are learning that age-old stock market rule: What goes up can come down.

After gaining 59% in its first two days as a public stock, Snap (SNAP) shares dove on Monday as several brokers came out with sell recommendations. They closed at $23.77, down 12% for the day and 19% off the high. The drop meant that anyone who didn't buy at the pre-trading IPO price of $17 was probably sitting on a loss.

Scott Kessler, an analyst with CFRA Research, says he was “surprised” to see it fall so quickly, but notes that can be common with new, hot stocks.

When people see a lot of hoopla over a new IPO, and “they don’t want to miss out,” that in turn causes a “lot of volatility,” which will continue, notes Kessler.

Millennials have largely stayed out of the stock market, held back by student loans, recent memories of the last crash and financial crisis, and a shortage of funds. Brokers and advisers had wondered, given Snapchat's popularity, if this IPO could entice them in.

The early answer: yes.

Online stock trading app Robinhood, whose core demographic has an average age of 30, says that Thursday was its biggest day ever, and that 43% of all its traders that day went for Snap stock.

“Snap’s IPO revitalized investing among the younger generation,” notes Baiju Bhatt, the co-founder of Robinhood. “We also saw a surge in new accounts, with many new customers opening up their first brokerage account."

The median age of Robinhood investors buying Snap on Robinhood has been 26, the same age as Snap CEO Evan Spiegel.

Chris Stearns, 30, who lives near Virginia Beach, bought 13 shares Friday morning because he sees Snap as the next Facebook.

“Snap is the first IPO-centric stock I’ve taken,” he says. “It’s a huge growth opportunity."

Stearns, who works with his dad putting in glass in homes and businesses, says that every person he’s hired over the past few years in their 20s was always on Snapchat.

“They use it constantly,” and their usage struck a chord with him.

Spencer Wilson, who lives outside of Flint, Mich. just turned 17, and he, too,  bought 20 shares of Snap.

"Every single one of my friends uses it," he says. "I think it will be really successful."

That brand loyalty drove Snap's younger investors to the stock, overriding concerns by many financial advisers that the unprofitable company, whose user growth started to slow at the end of last year, was more likely to follow Twitter's stock market travails than Facebook's success.

Zac Vineyard, 33, a web developer near Boise, Idaho, works for a local university, and being around the younger students convinced him about the power of Snapchat.

“It’s the only way I see people younger than me communicate,” he says. “Snapchat has clearly captured this audience in an engrossing way.”

A rebound in the stock could indeed entice more into the market, which is poised for more IPOs after a long hiatus.

Tim Edwards, 35, who lives near Chicago, bought 35 shares of Snap and is already looking ahead to the next big tech IPO, hoping to see ride-hailing apps Uber and Lyft and hotel alternative Airbnb in 2017.

And if not?

On Twitter, users described the scenario in fittingly visual terms: a roller coaster plunge.

Eshaghi says he too believes Snap is overvalued, but bought shares anyway because being involved with Snap's IPO "was memorable for me as a younger investor." He's not "too phased by the price fluctuations," and says that long term, "Snap will be fine because of their massive monetization potential."

Follow USA TODAY's Jefferson Graham on Twitter, @jeffersongraham, and subscribe to the daily #TalkingTech podcast on iTunes and Stitcher.