They’ve been some of the most coveted investments of recent years — pre-IPO shares of technology companies such as Facebook and Twitter — and the demand for them has spurred the emergence of a hot new private marketplace.

But some investors in that market have been duped, the Securities and Exchange Commission said Thursday.

In a series of enforcement actions, the SEC spotlighted hazards on stock trading’s new frontier. The actions came as the Senate is taking up legislation that would reduce regulatory requirements for companies seeking to raise money from investors.

Neither Facebook nor Twitter was accused of any wrongdoing.

Rather, the SEC alleged that various players involved in trading the private shares committed violations.

Frank Mazzola, 44, who allegedly created funds that raised tens of millions of dollars to invest in shares of the companies, was charged with civil securities fraud.

Among his alleged violations: telling investors his funds owned Facebook shares when they did not, collecting hidden fees and giving investors false information about Twitter’s revenue — a closely held secret that the privately held company was not required to disclose.

For example, according to the SEC, Mazzola sent an e-mail to a potential investor in 2010 saying that “we have several senior Twitter execs as clients and we have a very good comfort level that the rev for 2010 is north of $100 million.”

In fact, the SEC said, Mazzola had no information to support the revenue projection and no senior Twitter executives as clients.

Separately, the SEC filed administrative cases alleging that another investment manager, Laurence Albukerk, concealed information about his fees and that a firm called SharesPost provided an online platform to match buyers and sellers without registering as a broker.

“The newly emerging secondary marketplace for pre-IPO stock presents risk for even savvy investors,” Marc Fagel, director of the SEC’s San Francisco regional office, said in a statement.

The cases stem from a year-long SEC investigation of trading in shares of companies that have not yet undergone initial public offerings, or IPOs, the agency said.

But the cases may be noteworthy for another reason: the fact that there are not more of them.

No other charges are anticipated from the probe, SEC spokesman John Nester said.

IPOs allow shares to be traded on conventional stock markets. Before companies cross that milestone, investment funds can try to buy shares privately — for example, from former employees. Such investments are especially risky because investors don’t have access to the kind of detailed financial reports that publicly traded companies issue.

Neither Mazzola nor a lawyer the SEC said is representing him responded to requests for comment.

Without admitting or denying wrongdoing, Albukerk and his firm, EB Financial Group, agreed to give up $210,499 of alleged ill-gotten gains, including interest, and to pay a $100,000 penalty.

In a statement, EB Financial spokesman Ronald K. Low described the compensation as legally earned.

SharesPost and its president, Greg Brogger, neither admitted nor denied wrongdoing but agreed to pay penalties of $80,000 and $20,000, respectively, the SEC said. In an e-mail, SharesPost spokesman Jeremiah Hall said the company has acquired a brokerage firm and registered it with the SEC.

Mazzola, a resident of New Jersey, was a principal of Felix Investments and a manager of Facie Libre Management Associates, which were also charged.

Mazzola solicited investors by falsely claiming that Facie Libre was “Facebook-approved” and thus more likely to obtain Facebook shares, the SEC said. In reality, the SEC said, a Facebook attorney had warned Mazzola not to make any such claim.

At times, Mazzola was stymied in his efforts to acquire shares of Facebook and another company, Zynga, but allowed investors to believe otherwise, the SEC said.

“Strikingly, investors who purchased shares” in one of the funds “bought interests in a fund that held no Facebook shares,” the SEC said.