Charles Barfield, living on the streets for the past five years, doesn’t trust anyone.

Armed with a pocketknife, he beds down in a doorway in downtown LA every night, making sure no one’s nearby. “People might look normal, but they do weird … things,’’ said the ponytailed 58-year-old who sells loose cigarettes for a quarter.

As police and advocates urged homeless people to seek safety in shelters on Friday as news spread of an at-large serial homeless stabber, they face the challenge that many street dwellers like being alone because they feel it’s less risky or simply because they can’t cope with people due to mental illness.

With robberies, assaults or even rapes frequently occurring on the streets and in shelters, many homeless people have found that survival comes down to finding hidey-holes where no one can see them. But advocates for the homeless say that’s also what makes them easy marks for criminals looking for victims in general or homeless people specifically.

“People on the street know it’s dangerous, but many people want to be on their own,’’ said Herb Smith, president and chief executive of the Los Angeles Mission in Skid Row in downtown Los Angeles. “They’re not socialized. It’s part of their condition.’’

Warnings about the hazards of sleeping on the street were stepped up while police continued to hunt the perpetrator who recently knifed two homeless men and a woman in the back in the early morning hours as they slept. The first stabbing occurred July 3 in downtown Los Angeles, the only incident where a witness saw a suspect fleeing.

The second incident on Tuesday targeted a man as he slept on a bus bench in Santa Monica. The most recent was on Thursday, when a woman was stabbed in Hollywood. All three victims, who are in their 50s, survived.