Restaurant owners are also worrying about increased immigration enforcement: Nearly 20 percent of workers are foreign-born.

With unemployment at a 17-year low, businesses everywhere are struggling to find workers. Fast food is feeling the pinch acutely, especially as one important source of workers has dried up. In 2000, about 45 percent of those between 16 and 19 had a job — today it’s 30 percent.

“We used to get overwhelmed with the number of people wanting summer jobs,” Mr. Miller said, adding that he now gets maybe a handful of such applications, at most. “I don’t know what teenagers do all summer.”

Gavin Poole, a 17-year-old senior at Montville Township High School in New Jersey, likes the idea of being his own boss — that’s one reason he created a small business out of after-school landscaping and handyman work. The money has helped cover his cellphone bill and the payments on the Jeep Wrangler he leased last year. “I want to be prepared for the future, because you don’t know, financially, what situation you could be in,” he said.

A recent analysis by economists at the Bureau of Labor Statistics found that an increased emphasis on education — and getting scholarships — had contributed to the decline in working teenagers, reflecting both the rising costs of education and the low wages most people that age can earn.

Now, after years of benefiting from low-cost labor, many employers are starting to pay more. Fast-food wages began rising in 2014, and have increased faster than overall wages since. But at $10.93 an hour, the pay is still less than half the average for an hourly employee, pushing companies to offer more incentives — like dental insurance, sign-up bonuses and even travel reimbursement — to entice workers.