Philadelphia has a huge problem.

They are called “flash mobs.”

It is the latest spin-off from the social media we are awash in.

Teens post a message on their Twitter or Facebook accounts about a gathering, urging their friends and “cyber” friends to meet at a certain place.

Lots of them do just that. This weekend several thousand kids showed up on South Street after just such an invitation. There were no serious incidents.

That wasn’t the case in a couple of earlier cases. People were mugged; stores were ransacked.

Yesterday 10 teens were in court on riot charges stemming from one of the earlier incidents. They were all convicted. Another group will be in court today.

The city is mulling a curfew for young people. I’m not sure that is going to solve their problem.

I am sure of this: The city is battling serious fiscal issues, and exactly what they do not need right now is a real fear of anyone going downtown because of these “flash mob” hooligans.

They need to get a handle on his issue.

And fast.

Or they could find their economy – and that of any number of restaurants, nightspots, movies, museums and other destination points – going up in a flash as well.