Wild car meet-ups don’t just happen in Philly. They’re revved up on social media.

A series of wild car meet-ups across Philly that drew hundreds of spectators — and ended this weekend with the fatal shooting of 18-year-old Anthony Allegrini Jr. by state police — was not spontaneous.

An informal network of muscle car aficionados has for years used social media to promote similar gatherings — known as “takeovers” or “slide shows” — where participants shut down public streets to spin doughnuts or perform other stunts with souped-up vehicles.

A series of takeover events across the city early Sunday morning was promoted online under the slogan “Philly vs Everyone,” featuring tricked-out cars, fireworks, and even one man with a flame thrower device.

The gatherings, which included two assaults that were captured on video, culminated in participants shutting down I-95, near Penn’s Landing. According to police, Allegrini, of Glen Mills, tried to flee as two Pennsylvania State Police officers tried to disperse the highway rally, allegedly striking two troopers. One opened fire, fatally wounding him.

As of Monday, numerous similar events were still being planned in the Philly region in the coming weeks.

Regional accounts with such names as “Slideadelphia” or “Jersey Streets” routinely promote similar meet-up events, often in a minimally clandestine fashion in order to maximize attendance. Host accounts advise those interested in attending to RSVP by direct messages, and locations are then shared on the day-of to minimize the time police have to organize a response.

An event for later this month, called “Summer Bash,” is being advertised by an account named “Sliders Academy” and is cross-promoted by other groups in New Jersey and New York City. A customized promotional image for the event features images of cars in Center City and graphic design meant to resemble the cover art for the popular video game franchise “Grand Theft Auto.”

Another event, planned for July, is billed as a “send off” for Allegrini.

» READ MORE: A look at drag racing and car meetups in Philadelphia

Similar car rallies have a long history in the Philly region and elsewhere. While events like those seen earlier this week are illegal, other car meet-ups and drag racing events are organized in legal venues and occur without incident.

However, the popularity and visibility of illegal takeovers have grown in recent years, and local meet-ups have become popular enough to create a cottage industry of hangers on.

One entrepreneur has taken to selling tickets for takeover after parties at clubs or other event spaces. A community of amateur photographers and videographers have attracted thousands of followers by documenting the meet-ups, filming participants — or “sliders” — burning out, that drivers can in turn use to increase their own following.

At a news conference Monday about Allegrini’s death, police pledged to review video footage from the morning’s events to pursue charges against organizers and those filmed committing illegal acts.

As a likely result, word has gone out through the same channels. Some host accounts have locked down or begun deleting evidence of the events and the underlying network.

“If you posting vids dont tag sliders or hosts. Eyes on everyone,” read one post. “Law gonna start cracking down real soon.”

Since Allegrini’s death, others said they wanted to find more legal alternatives for the meet-ups.

“Philadelphia Police I know you are watching this page,” read another post. “Please give us the resources to get a legal place to do what we love and make sure last night never happens again.”

An earlier online version of this article gave the incorrect day when the shooting took place.