Salvador Vergara was so eager about GameStop Corp. in late January that he took out a $20,000 personal loan and used it to acquire shares. Then the buzzy stock dropped almost 80%.GameStop’s volatile ride is hitting the portfolios of individual investors such as Mr. Vergara who acquired the stock in a social-media-powered frenzy. These casual traders say that GameStop was their “YOLO,” or “you only live once,” trade. They acquired around its late January peak, betting it would continue its skyrocketing climb. While some cashed out before it crashed, others who held onto their shares are in the red.Mr. Vergara, a 25-year-old security guard in Virginia, started investing four years ago after deciding he wanted to retire young. To save money, he drives a 1998 Honda Civic, eats a lot of rice and lives with his dad. He stashed his savings mostly in diversified index funds, which are now valued at roughly $50,000. Then Mr. Vergara, a longtime reader of the WallStreetBets page on Reddit, saw others posting about buying GameStop shares and the stock’s colossal rise. He didn’t want to touch his index-fund investments, so instead he got a personal loan with an 11.19% interest rate from a credit union and used it to fund most of his GameStop purchase. He acquired shares at $234 each. GameStop shares started this year around $19, skyrocketed to almost $350 (and almost reached $500 in intraday trading) in late January, and then started to spiral back to earth. The shares closed Friday at $52.40, down 85% from the peak close. He plans to hold on to the shares because he is convinced in the company’s comeback.