Business and civic leaders in Chicago are calling on the administration of Mayor-elect Brandon Johnson to enforce a weekend curfew after hordes of unruly teenagers ran amok on two separate evenings over the weekend, terrorizing tourists and vandalizing cars and shop windows.

The president of the Rogers Park Chamber of Commerce, Bill Morton, an unsuccessful candidate for alderman in February’s municipal elections, said at a Sunday news conference that the crime exemplified by the violence Friday and Saturday nights is driving away business and investment in the city.

“I very much hope that our next mayor will take some measures to solve this issue of violent crime in our city,” Mr. Morton said, according to NBC’s Chicago affiliate station. Rogers Park is nine miles north of Chicago downtown loop, where the weekend unrest occurred.

On both Friday and Saturday nights in separate locations at downtown Chicago, hundreds of teenagers responding to social media posts about a “teen takeover” became unruly and began damaging cars and property despite a heavy police presence. Chicago police said 15 people were arrested in Saturday’s melee near Millennium Park, nine adults and six minors. Two teens were shot Saturday, as well as another Friday during a similar disturbance near the 31st Street Beach.

Videos circulating on social media over the weekend showed the throngs of teens jumping on vehicles, smashing windshields, brawling in the streets, and damaging city buses. Police were forced to escort terrified tourists to their cars in a garage near Millennium Park, and shots can be heard ringing out on several of the videos.

In a statement released late Sunday, Mr. Johnson — who will take over from the current mayor, Lori Lightfoot, in May — condemned what he called the “destructive activity” but blamed the chaos on systemic issues in the city.

“It is not constructive to demonize youth who have otherwise been starved of opportunities in their own communities,” Mr. Johnson said. “Our city must work together to create spaces for youth to gather safely and responsibly, under adult guidance and supervision.”

Ms. Lightfoot, who lost her bid for re-election in part because of concerns about runaway crime in the city, said the city has invested millions of dollars in community-based support for teens but that parents also need to step up and make sure their children stay out of trouble.

“Parents and guardians must know where their children are and be responsible for their actions,” Ms. Lightfoot said in a statement. “Instilling the important values of respect for people and property must begin at home.”

Following similar disturbances last year and a string of violence that culminated in the fatal shooting of a 16-year-old, Ms. Lightfoot banned unaccompanied minors from Millenium Park on weekends and changed an existing curfew — on the books for more than a decade — that is supposed to keep teenagers off city streets after 10 p.m. on weekends. Mr. Morton and others at the Rogers Park news conference called on police officials to enforce these existing laws.

In a trend mirrored in other big American cities, Chicago has seen a spike in overall crime over the past two years. Violent crimes such as murder and criminal sexual assault have been steady or declining since 2021, according to Chicago police department figures, but petty thefts such as robbery, theft, and motor vehicle theft have skyrocketed. So far in 2023, motor vehicle theft is up 135 percent over the levels seen in 2022 and 230 percent higher than in 2021.