I suspect most just choose to disconnect from their friends and relatives. Perhaps they don’t get on them, maybe they’re struggling with depression or have done something they’re ashamed of and can’t face the people they know. Perhaps they’ve got in with a crowd of people and don’t feel the need to connect with their family or friends and then eventually, it’s been so long, they don’t know how to reconnect.

Kids leave home and disconnect from their families often. I think it’s part of the angst of being a young person. It’s sad. Sometimes they may have been kicked out by the family or perhaps they just don’t feel they fit.

And yes, some people probably have been abducted, murdered and so on, but I hope they are in the minority.

As to protecting yourself, the biggest danger comes from people we know (and I don’t think you should be freaking out because this ‘biggest’ danger, isn’t so big). Let your family or friends know where you’re going if you go for a walk on your own. If your instincts tell you a person is unsafe, listen to them. Really though, the chances of you going missing without you choosing to do so are slim.

Now go and listen to some of this happy music!

In addition to kidnappings, murders, driving off cliffs, into water, getting stuck in a well or whatever, there are also people who disappear because they don’t want to be found (oh, as @Earthbound_Misfit just finished answering!).

I would recommend taking a self-defense course, certainly one that explains awareness and effective things to do in possibly dangerous encounters, and possibly (after that) also one that teaches some physical self-defense techniques as well.

You might find this article in the Washington Post comforting.

”.. children taken by strangers or slight acquaintances represent only one-hundredth of 1 percent of all missing children. The last comprehensive study estimated that the number was 115 in a year.

Far more common are children who have run away, have gotten lost or injured, have been taken by a family member (usually in a custody dispute) or simply aren’t where they’re expected to be because of a miscommunication. The only scenario more unusual than stereotypical kidnapping is when families falsely report a child as missing to disguise murderous deeds.”

On the other hand there’s a lot of mystery surrounding people who go missing at US National Parks, and though you can find the information on who, what, where, when if you look for it, this doesn’t seem to receive as much publicity as it maybe should.

Sometimes, people are “missing” for a very long time due to incompetence by the local authorities.

A few years back, three salesmen were here for a convention, and just vanished. During the months that followed, more than one person contacted (and even visited in person) the county police and suggested that they might search a small man-made lake near which a road with almost no lighting made a sudden 90-degree turn just before it.

People were very adamant: “I came SO CLOSE to driving into that lake…..please have somebody check there….”

Nobody ever did, even though this lake was not very far from the Convention Center.

Months later, some regular citizen was out there on his boat, messing-around with some kind of sonar gear, and detected a car, not too far below the surface.

The families and friends of those three guys had to wonder and suffer for many months due to nothing more than casual professional ineptitude.

Number of law-enforcement personnel held accountable:

Zero.

We had a similar case here. An 18 year old left home to meet friends at myrtle beach. He never arrived. No clue as to where to look. 10 years later they were putting a new gas line in the bottom of the river in the town he lived in. They found him in his car at the bottom. It was at a tricky turn also.

^Yeah. I’ve heard of dozens of similar incidents… When I used to sell kayaks, and canoes, I advised people to always tell someone where they were going to be paddling, and when they should be expected back. At least then, they have a starting point to begin a search…. I think that’s why that guy had to cut his own arm off, when a rock crushed it in a desert cave. Nobody knew he was there…

Yeah, it made me kind of happy that in his more recent movies, James Franco has his arm back again…

Well, human trafficking is a big problem. Women, especially when on their own, are captured and sold into slavery, often sex slavery. According to this site, 3,287 people go missing every day, mostly women and children.

Speaking of movies, Drag Me To Hell (2009), what happened to Christine Brown isn’t very comforting, but had her boyfriend not witnessed it at the end of the movie, no one would have known.

It happens more than you would think. People disappear from parking lots, camp sites, national parks, even from busses and trains. Some are very mysterious and hard to explain, some are not so much so. As in the case of Jimmy Hoffa, the Teamster Leader who in all likelihood was whacked by the mob. I’ve even read tales of people disappearing without trace off of cruise ships. All I can say is use some discretion and common sense, be alert and aware of your surroundings, and get you some pepper spray. And don’t go anywhere that you are unfamiliar with after dark.

Make sure somebody knows where you are going. You could send a text, “On my way to Parker’s Grocery. Call you when I get home.”
That much gives police a place to start if you did go missing.
Having someone with you helps.
The worst thing you can do is look scared, timid. Predators eat that like candy.
Look confident, and in a hurry.
Be aware of your outs; businesses, homes, public areas you can get to quickly to be safe if you feel threatened.
Don’t try to hide. Staying in shadows is a bad idea.