Robinhood’s shares jump as much as 65 percent, like the meme stocks it enabled.

Robinhood, meme thyself.

The stock trading app that helped fuel a frenzy by small investors earlier this year soared on Wednesday in trading that had all the hallmarks of the “meme-stock mania” that drove up prices of companies like AMC Entertainment and GameStop.

Robinhood’s shares rose as much as 65 percent to $77, double their price at the end of last week, and trading was briefly paused by the Nasdaq stock exchange. By midmorning, the shares had fallen somewhat and were up about 44 percent. It was a second day of sharp gains after jumping 24 percent on Tuesday.

Robinhood became a publicly traded company only last week. It priced its initial public offering at $38 a share, but the stock stumbled in its first day of trading on Thursday, finishing down more than 8 percent.

Since then, however, buyers have emerged, especially among the ranks of individual investors that the company caters to. On Wednesday, the stock shot to the top of Fidelity’s list of orders from the traders at its brokerage unit, suggesting that demand from day traders is driving the surge in the shares.

Ark Invest, the money management firm run by the social media-savvy stock picker Cathie Wood, has also been buying shares of Robinhood for the exchange-traded funds that serve as her investment vehicles. Daily disclosures of her holdings — which are closely followed and sometimes mimicked by day traders — have shown her buying more than 1.5 million shares of Robinhood, giving her a stake worth over $100 million at the peak of Wednesday morning’s surge.

Here’s what else is happening in markets today:

• The S&P 500 was down 0.3 percent in midday trading Wednesday. The Nasdaq composite was up about 0.7 percent.

• The Stoxx Europe 600 closed with a 0.6 percent gain.

• Oil prices continued to fall, with West Texas Intermediate, the U.S. crude benchmark, down as much as 3.5 percent to $68.06 a barrel.

• Spirit Airlines said it expected flight cancellations to ease by Thursday. The airline canceled more than 60 percent of flights on Tuesday and had scrapped about 60 percent of Wednesday’s flights as of midday, according to the flight-tracking website FlightAware. Spirit said in a statement that it had done a “thorough reboot of the network” and blamed the disruption, which began over the weekend and has affected hundreds of flights each day, on “overlapping operational challenges including weather, system outages and staffing shortages.” The airline’s shares were down about 4 percent in midday trading.

• Lyft fell about 9 percent in early trading on Wednesday. Despite reporting strong growth for the second quarter on Tuesday, lost $251.9 million. Uber is set to publish its second-quarter financials after the markets close on Thursday.

• Shares of General Motors fell more than 8 percent in midday trading. The company reported a jump in profit in the second quarter, but G.M.’s chief executive, Mary T. Barra, said a global shortage of computer chips would continue to be a problem until next year.