Gary Zabroski started working for General Electric Co. in 1976, at an aviation factory in his hometown of Lynn, Mass. The job paid well, came with benefits and, for Mr. Zabroski, provided a career ladder for a man with a high- school education who started out cleaning toilets.

“You had a job for life if you had gotten in there,” said Mr. Zabroski, 61 years old. He rose to punch-press operator and retired in 2016, after working 40 years at the century-old plant, which roared to life during World War II and still churns out engines for jets and helicopters. He left GE with an annual pension of $85,000 and company stock valued at more than $280,000.

Retirement looked pretty good until GE shares collapsed. His shares are now worth about $110,000, prompting a late-life job hunt. “I never planned on retiring and having to go back to work,” said Mr. Zabroski, who has monthly mortgage payments and supports a partially disabled wife. “It’s kind of scary.”

The rapid unraveling of GE has wiped out roughly $140 billion in stock-market wealth in the past year, not just at big Wall Street firms but among small investors. The industrial giant is one of the most widely held U.S. stocks.

By comparison, the stock value lost by GE in the past 12 months is twice the amount that vanished when Enron Corp. collapsed in 2001—and more than the combined market capitalization erased by the bankruptcies of Lehman Brothers and General Motors during the financial crisis. Longer term, GE’s market capitalization has fallen more than $460 billion since its 2000 peak.