But traders like Ms. Crum, who lives in Sunrise Beach, Mo., are making an earnest effort to do it right.

Every night, she meticulously compiles a list of the stocks she’s watching using different measures. One of them, an online tool called a volume scanner, filters out stocks that are being traded more or less than usual, which she believes can tip her off to a good bet. And she tries to mitigate her risk: Ms. Crum uses stop-loss orders, to sell a stock when it hits a certain price, and limit orders, which let investors set more specific instructions.

Like many other young traders, she’s big on sharing what she learns — usually in TikTok videos to her 163,000 followers. Ms. Crum posted one about candlestick charts, which illustrate the price range of a holding on a particular day. In another, she explained how to use relative strength index, or R.S.I., which measures price changes over time and can indicate when a stock might be oversold or overbought.

“I started out doing swing trades, an old reliable way to go about trading,” Ms. Crum said, adding that she’ll day-trade if she spots something that appears to be “an obvious winner.”

Like other young investors, she is riding a wave that would not be possible without the widespread adoption of commission-free trading in late 2019, which threw open the doors to those without deep pockets. Retail trading now accounts for roughly 22 percent of all trading volume, according to Piper Sandler, a financial services firm, up from 13 percent a year ago, when overall volume was also lower.

“There are days when I make 100 trades or more,” said Dan Knight, 26, a day trader who co-hosts a podcast about the stock market. “I would have never been able to trade with $7 commission fees.”

Mr. Knight’s podcast, “P.G.I.R.,” was recently among the top 50 business shows on Apple podcasts in the United States and ranked as the top investing show in early February, according to Chartable. Irreverent and sprinkled with profanity, every episode starts with a voice-over from the rapper Flavor Flav, and Mr. Knight is introduced as the Deity of Dips, while his co-host, Mitch Hennessey, goes by Hugh Henne — a nod to his grandfather’s first name and, playfully, to Hugh Hefner.