Community Facebook sites are a great way for neighbors to instantly exchange information, trade unwanted junk and advertise yard sales. They are knowledge purveyors, gossip mills, safety promoters or paranoia generators, depending on the day and subject.

I was perusing the Medlock Park neighborhood site last Monday (I joined it to keep track of annexation efforts there) and noticed that a young, mixed-race guy was admonishing neighbors for calling the cops on him.

Tony DeAngelo, a 24-year-old videographer who grew up in the central DeKalb County community, wrote: “To All My Neighbors. ESPECIALLY the ones who live by the Nature Preserve. Just because you see 5 black guys walking through it doesn’t mean you have to fear for your life and call the police.”

“This is NOT the first time it happened,” he added. “I just wish people wouldn’t jump to conclusions or be all extra paranoid. I helped build that preserve when I was a kid.”

The day before, DeAngelo went to the preserve to shoot footage of a local rapper named Snypa. DeAngleo figured the woods where he once played would give the video an outdoorsy, artsy feel. The group parked two cars at the entrance — it’s across from several homes — and walked in.

Did they look menacing, in a gangsta-rap kind of way?

“No, we were dressed casually, shorts and T-shirts,” DeAngelo told me as we walked the woods last week. “I guess the artist (Snypa, that is) was dressed most intimidating.”

How’s that?

“He had on skinny jeans and a black vest,” he said.

I dropped my notebook and clutched my wallet. You can never be too careful in environments that attract rappers in skinny jeans.

On the day of the video shoot, a cop pulled over one of the two cars as they drove away from the nature preserve. Two more police cars arrived. And then, to make this a full-blown incident, a fire engine rolled up.

The cops were firm but polite. They checked for IDs and said someone had called “because they were scared.”

The Facebook site for the mostly white neighborhood started buzzing after DeAngelo’s initial post about the incident. Folks started apologizing and castigating those who harbor racist thoughts. The Medlock neighborhood is directly north of Decatur, which has more concentrated white guilt than most any other Georgia burg. Medlock is probably not far off.

I read the thread of comments with interest, because the issue of racial perceptions and misperceptions is front and center in the national conversation.

“What I wouldn’t do to stop this obscene racism!” one neighbor wrote.

As I read these comments Monday morning, the site suddenly went through a whipsaw.

At 10:35 a.m., a man cutting his lawn was robbed at gunpoint. A few minutes later, a man was robbed walking his dog. And then a woman was robbed.

“I was also just robbed at gun point while walking my dog at Woodridge and Medlock intersection,” the woman noted on Facebook at 11 a.m. “They took my phone. Two African American men driving the blue sedan. Be careful.”

A few minutes later another woman chimed in, “Guess what!! There were just 2 separate robberies at gunpoint by 2 black males in a SUV!!!”

The posts took on a different tone.

“Perhaps being suspicious of strangers in the neighborhood shouldn’t be ridiculed as it was recently,” a woman wrote.

Another, who had been burglarized before, wrote, “If I see someone suspicious, I’m not going to sit back and try to sort it out. I will call the cops. When it comes down to statistics of crimes you have your answer why cops are called more on an African male than a white male. Bottom line.”

“Yea,” DeAngelo responded. “The two biggest stories on the news right now is a white guy killing 9 people at a church and two murderers escaping prison.”

Police responded in force to the Medlock robberies, quickly blocking numerous entrances to the neighborhood as a helicopter searched overhead. But the gunmen, driving a sedan carjacked two days earlier, were gone. One neighbor told me the crooks were almost caught because they got greedy, going for the third stickup. “If they went for a fourth, they would have been caught,” the man told me.

Eric Wallin, one of the robbery victims, wrote a long, thoughtful dissertation on getting robbed. His said his first thought when he saw the gun aimed at him was: “Wow this is going to be inconvenient to have to go to the DMV and be without my phone.”

Wallin, a computer programmer who has lived in Medlock just six months, added that it’s prudent to just go along with a gunman’s demands — unless he tells you to get in the car. He said he does not feel unsafe.

In an interview, Wallin gave his take on the role of Facebook and other platforms in building community: “Social media at the neighborhood level is extremely powerful when there’s open channels like this,” he said. However, he added, “I think (the mini-crime wave) was an unfortunate thing for Tony. I don’t think it helps him make his point.’

Lisa Crowder, a lifelong Medlock resident who works as a real estate agent and runs the Facebook site, noted that the discussion “went full circle in a short period.”

The site is amazing in weaving residents together. A few weeks ago, it helped an owner locate a lost dog within minutes.

But the always-on sense of interconnectedness, the repetitive drumbeat of crime stories, the constant sightings of “suspicious” cars and people ends up sinking in.

“We have so many points of info coming in about what is suspicious that it just feeds hyper-vigilance,” Crowder said. “You hear about every little thing, and so we get more and more paranoid. When you see everything as potentially frightening, then everything becomes suspicious.”

Not long ago, police were called to a report of someone stealing mail in the neighborhood. Instead, it was a woman returning a book to a free library in front of someone’s house.

Another resident followed a suspicious car driving slow. Turns out it was an old woman trying to find a relative’s home.

And police were called check on a prostitute roaming the streets in the middle of the night. It was a resident catching some night air after returning home from dancing.

The trick, of course, is to make the distinction between “suspicious” characters and folks you just don’t happen to know.

In that vein, one resident used the Facebook page to invite residents to actually behave socially in the flesh: “I’m making a commitment to have a driveway party next Friday after the 4th. I will have beer, beer and icey pops. Maybe I’ll throw in some bubbles and sparklers too.”

Prostitutes in slow moving cars, watch out!