For years, Cheryl Dopp considered the ding on her phone from a new Airbnb Inc. booking to be the sound of what she called “magical money.” A property she rented out in Jersey City, N.J., on Airbnb could gross more than $8,000 a month, she said, double what long-term tenants would pay.

Now, Ms. Dopp associates the dings with cancellations and financial misery. The 54-year-old information-technology contractor said she had about $10,000 in bookings evaporate overnight in March. She has $22,000 in monthly expenses for a largely Airbnb portfolio, she said, that included another Jersey City home and a house in Miami.

In her mind, the promise of more rental income offset the growing debt, she said. “I made a bargain with the devil.”

Ms. Dopp is part of an upper-crust dimension of the gig economy: property owners and speculators who bought or leased real estate in pursuit of Airbnb profits. Airbnb spawned a cottage industry of homeowners running their own property empires, turning the startup into a hotelier without any hotels.

The coronavirus’s spread has exposed swaths of the U.S. economy that were ill-suited for a crisis—great for offering inexpensive goods and services quickly, terrible in an economic disaster.