RealMoney

Coming off of a difficult 2015 in which his fund lost 20% and one of his kids suggested he long his shorts and short his longs, David Einhorn's Greenlight Capital just announced a stake in Yelp (YELP) and a long play on natural gas. Might these be the positions he discusses at Wednesday's Sohn Investment Conference in New York?

"The stock has suffered due to missed expectations and anxiety about an upcoming negative documentary," Greenlight Capital wrote in a letter to investors. The documentary Einhorn references is called Billion Dollar Bully and it alleges that Yelp, the online review service, uses mob-like techniques to extort protection money from businesses harmed by negative (and perhaps false) reviews. Shares of Yelp are down 45% over the last year, which is roughly when news of the documentary was reported.

Einhorn also made a bet that the price of natural gas will soon rise, according to the letter. This long view on natural gas plays off of his current holding of coal and natural gas producer, Consol Energy (CNX).

If these new investments play out -- and they end up being the ones Einhorn discusses Wednesday at Sohn -- it couldn't come at a better time.

At last year's Sohn Conference, Einhorn announced his short position in Pioneer Natural Resources (PXD) in a presentation in which he called the oil and gas company a "mother fracker." Shares of the company are down 0.3% over the last year, though shares fells as much as 30% at times during that period. Greenlight maintains its short position on the company and said that stock's relative positive performance is due to the disconnect between management presentations and more sobering filings with the Securities and Exchange Commission.

In 2014, Einhorn presented a short position in AthenaHealth (ATHN), calling it a bubble stock. Shares of the company are down 0.5% in the two years since the 2014 Sohn Investment Conference.

Some of Einhorn's other recent picks haven't fared well, either.

In his year-end 2015 letter to investors, Einhorn acknowledged that his fund was short two of the best-performing stocks in the S&P 500, Netflix (NFLX) and Amazon (AMZN), and long two of the worst performing stocks, Consol Energy and Micron Technology (MU).

Einhorn has also been badly bruised by his long play on beleaguered renewable energy company SunEdison (SUNE). In October 2014 Einhorn said at another investment conference that the then-$17 stock could go as high as $32. He wasn't entirely wrong, the stock hit those levels last July. Unfortunately, the stock crashed dramatically over the past year and the company filed for Chapter 11 protection last month. Einhorn still maintained a stake in the company all the way down but said in his letter to investors: "Obviously, we underestimated the fragility of the situation." 

On the heels of a difficult 2015, it will be interesting to see how Einhorn presents his latest picks at Wednesday's Sohn Investment Conference.

The Sohn Investment Conference, which will be held in New York on May 4, 2016, brings together some of the top minds in the financial world for a day of sharing investment ideas. It is held in honor of Ira Sohn, a Wall Street professional who lost his battle with cancer when he was 29. Proceeds from the New York conference, as well as other conferences the Sohn Conference Foundations holds, are dedicated to the treatment and cure of pediatric cancer and other childhood diseases. The foundation has so far raised more than $65 million.