In a rare move, Nasdaq Inc, Intercontinental Exchange Inc's New York Stock Exchange and the Financial Industry Regulatory Authority (FINRA) published notices about manipulation and fraud tied to market debuts.

Some investors harmed by the pump-and-dump schemes appear to be victims of an evolving social media scam called "pig butchering," Finra said.

"These schemes sometimes begin with a seemingly misdirected text message or message on a social media messaging application leading to a relationship (sometimes romantic in nature) between victims and bad actors," Finra said.

Once a relationship is formed, the scammer recommends the victim place limit orders in certain securities at specific times and prices.

Finra said most of the price spikes it observed involved IPOs of small-cap issuers with operations outside the United States.

The IPOs typically raised less than $25 million, valued the firms at under $100 million and issued fewer than 20 million shares.

There has been a spate of unusual post-IPO price pops this year, including many China-to-U.S. offerings, such as Magic Empire Global, which soared over 5,000%, and fintech AMTD Digital, which tripled in price in a week.

Finra also said it was investigating accounts opened for foreign nationals at U.S. broker-dealers to invest in IPOs that later placed manipulative orders and trades to inflate aftermarket prices.

The NYSE and Nasdaq said they were probing the underwriters of the IPOs to ensure they did proper due diligence on registration statements.

"When gatekeepers such as underwriters engage in misconduct or otherwise are derelict in their duties, confidence is diminished and investors suffer," Nasdaq said.

(Reporting by John McCrank; Additional reporting by Lance Tupper; Editing by Josie Kao)

By John McCrank