Avonte Oquendo, 14, was last seen one week ago, skipping away from his Queens, N.Y., school. The group Autism Speaks is offering a $70,000 reward for his safe return. NBC's Katy Tur reports.

The characteristics of autism, long thought of as a mystery, turn from enigma to life-threatening dangers when autistic children go missing, experts say.

Family members of Avonte Oquendo, a 14-year-old non-verbal autistic boy who vanished a week ago from his Queens, N.Y., school, are hoping his story will be one of the happy ones. But law enforcement face a multitude of challenges in Avonte's situation that they wouldn't normally have in a missing child case: For starters, Avonte can't respond when his name is called.

"They sometimes will seek tight enclosed spaces and hide from searchers. These are not going to be a typical search for a child, as you might think, especially in a densely populated area like Queens," said Bob Lowery, senior executive director for the missing children division at the National Center for Missing & Exploited Children.

"This child is not going to be out looking for help," Lowery said. "He might be reacting much differently. He might be eluding people."

Avonte may also not have the ability to care for himself, said Lisa Goring, vice president of family services with Autism Speaks, an advocacy organization.

"A 14-year-old in general is still a very young person, so that obviously is a cause for concern, being on his own," she said.

More worrisome, children with autism often engage in "high-risk behavior," Lowery said, such as gravitating toward active roadways and bodies of water. For children with severe autism who "wander," or bolt from safe environments, as Avonte did, about 91 percent of them who die are killed by drowning, he said.

This year alone, 14 kids with autism have wandered and died, according to the National Center for Missing and Exploited Children.

But the stories don't always end in tragedy. In October 2011, a non-verbal autistic 8-year-old in central Virginia, Robert Wood Jr., was found alive after missing for nearly a week. Robert had wandered away from a park while he was with his family and was found curled up in a creek bed.

"There were an estimated 6,000 people searching for him and there was never a credible sighting of him. The children are extremely clever about the way they elude. You can't underestimate a child with autism," Lowery said.

Searchers will be paying especially close attention to small spaces that Avonte could have climbed into.

"We don't fully understand why they seek these tight enclosed spaces, whether it's for security for comfort or their trying to escape maybe some noises or stimulus that may frighten them or irritate them," Lowery said.

The week-long search for Avonte has been fraught with false hopes and tips that didn't pan out. The boy was last seen running from the Riverview School in Queens onto the street on a school surveillance video; few other clues have poured in.

His family said Avonte likes trains, so police have homed in on subway stations, posting fliers throughout the system.

If a volunteer or a stranger does spot Avonte, Goring recommended following him, but not approaching him, to avoid scaring him.

"Call the tip line to let them know. Follow or keep an eye on Avonte but don't necessarily approach or touch him. Keep him in your sight and communicate with law enforcement," she said.

In runaway cases where autism isn't a factor, law enforcement have other worries on their minds.

"The great majority of our missing children are going to be runaway children. They want to be away and they don't want to be found in some cases, and naturally we are concerned about their welfare as well," Lowery said. "They've got to sustain themselves while they're out there so they're often times vulnerable to exploitation or someone wants to take advantage of them. Lot of our children in sex trafficking start out as runaway children."

Regardless, law enforcement always spend time with the family to find out what the child's particular interests are — something they did in Avonte's case, which led them to discover his affinity for trains.

While no statistics on how many children with autism wander are available, Lowery said it appears to be seasonal: More leave home when the weather is warmer.

"We're not going to give up searching till we find Avonte," Lowery said. "No one is giving up on Avonte. We're going to continue looking until he's found."

The family feels the same way.

"We get leads throughout the day, and whenever we get them, we try to take them seriously," Avonte's brother, Danny Oquendo, told NBCNewYork.com. "We call police detectives, then volunteers who go to that area."

Added their father, Daniel Oquendo, "We can't even sleep. It's hard to sleep knowing your child is out there and he could be cold and hungry and he can't even communicate."

A $70,000-plus reward is being offered for Avonte's safe return, according to Autism Speaks, which has joined the family in its search efforts.

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