Robinhood Market’s largest source of revenue more than tripled in the first quarter as the trading app became immensely popular with young investors amid the meme-stock frenzy.

Revenue from “Payment for order flow,” a system where market makers like Citadel Securities pay retail brokers including Robinhood for routing orders to them, reached about $331 million in the first quarter, up from $91m a year ago, according to an analysis of a securities filing.

Within the first quarter, revenue from payments for order flow peaked in February at about $121m, before dropping 20 per cent to $96.7m in March.

Robinhood’s co-founder and chief executive officer, Vlad Tenev, had testified that the practice is the company’s largest source of revenue.

Critics including US lawmakers and a state securities regulator have said Robinhood makes investing real money feel too much like a game.

In response to critics, Robinhood has said its platform doesn’t encourage excessive trading and fills a crucial role in financial markets by helping a young and diverse group of traders to invest.

At Berkshire Hathaway’s annual meeting Saturday, Warren Buffett weighed in on the Robinhood phenomenon, saying the app has become a big part of the “Casino aspect” of the stock market recently.