NEW YORK (Reuters) - EBay Inc.’s stock price slumped for most of last year but a number of prominent hedge funds were so convinced that change is on the horizon for the e-commerce company that they established new or added to existing positions in the last months of 2018.

FILE PHOTO: The eBay app is seen on a mobile phone in this illustration photo October 16, 2017. REUTERS/Thomas White/Illustration

Baupost Group, run by Seth Klarman, and BlueMountain Capital both made new investments while Hudson Bay Capital Management and Adage Capital Partners expanded their bets with sizable purchases during the fourth quarter, regulatory filings and data compiled by Symmetric.io show.

Banking giants UBS AG, Citigroup Inc, JPMorgan Chase and Morgan Stanley, which invest for retail and institutional clients, also purchased millions of new shares, the data show.

For these investors, the nearly 30 percent gain in eBay’s share price in the first seven weeks of trading this year represents a sizable windfall that was likely fueled by behind-the-scenes moves of two activist hedge funds that also built stakes recently.

Elliott Management, one of Wall Street’s busiest and successful activists, said in its regulatory filing that it made a new bet on eBay in the fourth quarter, listing call options on 8.5 million shares. In January, Jesse Cohn, a partner at Elliott and head of its U.S. Equity Activism, wrote to eBay’s board to urge a sale of StubHub ticketing and its classified-ads business, forecasting that doing so could help push the stock price to as high as $63 a share in 2020. It closed at $36.32 on Thursday.

Starboard Value, another prominent hedge fund which has won more board seats through settlements than others, also built a stake and contacted management, people familiar with the move said, even though eBay was not listed on Starboard’s filing.

Starboard did not respond to questions about the position.

The 13-F regulatory filings that require fund managers to detail the amount of stock they held in U.S. companies at the end of the previous quarter often do not require filers to disclose derivatives, which means an investor can build a position without its showing up on this filing.

Ebay on Thursday announced a restructuring plan that will unite geographic regions under a global segment and said that a senior executive, Scott Cutler, will leave.

Baupost’s 13-F filing shows that it bought 21 million shares of eBay in the fourth quarter, making the company one of eBay’s top five U.S. holdings.

To be sure, there were also hedge funds that backed away. Larry Robbins’ Glenview Capital Management, which boasted a 17 percent gain in January after losing 16 percent last year, sold 4.4 million eBay shares, cutting its position by 37 percent.