Einhorn's Greenlight Capital invests in Yelp, natgas

Hedge fund manager David Einhorn on Monday told investors he had made new investments in natural gas and in business review site Yelp but has exited positions in Greek banks and financial services company Delta Lloyd.

The head of Greenlight Capital said Yelp could double its revenue by 2019, according to his first-quarter letter to investors, which was seen by Reuters. The news helped push up Yelp's stock price more than 6 percent in premarket trading.

Yelp's stock has "suffered due to missed expectations and anxiety about an upcoming negative documentary," the fund wrote in the letter, adding however that it does not expect the film to have a negative impact on its investment thesis and that if Yelp should ever decided to sell, a bidding war would emerge. "We rate them five stars," Einhorn wrote, referring to the company's own one to five star rating system.

Einhorn is widely followed in the secretive hedge fund industry and his letters are often seen to give hints for successful new investment trends.

Traditionally he invests in stocks but he wrote that he has now taken a "macro position" in natural gas, expecting that prices will climb. Inventories are still high after a record warm winter and over-drilling, but Einhorn said cooler temperatures and lower production "could lead to a shortage within a year."

Adam Jeffery | CNBC

David Einhorn, founder of Greenlight Capital.

A year ago Einhorn laid out a case against oil frackers at the Sohn Investment Conference. He will be speaking at the Sohn conference again later this week.

Greenlight's portfolio has climbed 3.1 percent in the first four months of 2016, beating many hedge fund rivals and the broader stock market. It marks a turnaround after last year's 20 percent loss, Einhorn's first down year since 2008.

Hedge funder David Einhorn scores with fracking bet

During the first three months of the year, Greenlight said CONSOL Energy and retailer Michael Kors Holdings helped boost returns. A gain in gold prices and Greenlight's "bubble basket" of shorts, which dropped 13 percent, also helped returns.

The biggest losers were Japanese financial company Resona Holdings and renewable energy company SunEdison , which filed for bankruptcy.

Einhorn also told investors that the firm had reinitiated a position in Hatteras Financial which he'd owned previously.

He also said he closed investment positions in financial services company Delta Lloyd and exited investments in Greek banks, "at almost a complete loss."

— CNBC contributed to this report.