LAS VEGAS >> A teen was swept away in a drainage wash in the Las Vegas area and remained missing, and two people were rescued from a van stranded in high water in suburban Phoenix after heavy rains in the Southwest flooded ditches and roads.

Family and friends gathered today in Henderson, southeast of the Las Vegas Strip, to look for a 17-year-old boy who disappeared after falling into a flood channel the day before. The wash had filled quickly after a Wednesday morning downpour.

William Mootz was hanging out with friends when he somehow fell into the Pittman Wash, which meanders past a shopping mall and his high school, police said. The teen apparently didn’t intend to get in.

“I think they were just going out there to look at the raging water in the washes,” Henderson police spokesman Keith Paul said.

Family members say the incoming high school senior is a strong swimmer and has emergency preparedness experience.

More than a dozen Henderson police officers walked up and down the wash with guidance from city public works employees who know how water typically flows down the channel. In all, about 100 volunteers were helping 40 police, firefighters and city employees look for Mootz.

They cleared an estimated 15 tons of dirt and debris from a more than mile-long, concrete-lined portion of the wash before turning their attention to a wider, muddy marsh farther downstream. Rainwater in the wash ultimately drains into Lake Mead.

The Las Vegas Metropolitan Police Department was helping the effort with a helicopter. The chopper was being used to fly searchers into otherwise inaccessible parts of the mucky wetland.

“More than anything else, it’s the use of the Metro Police helicopter that’s very helpful in searching a large area quickly,” Paul said.

In the Phoenix area, flooded roads led to a dramatic rescue Thursday morning. A driver and her disabled passenger had to be pulled from a medical transport van that was stranded after the driver tried to navigate a flooded Scottsdale wash.

Firefighters used a ladder truck, and news video showed the driver and passenger climbing out of a van stopped in the middle of a flooded area.

On Wednesday, three young men were spotted riding an air mattress down floodwaters in Henderson.

The shirtless trio cheered and waved to a KTNV news helicopter crew as they rode the makeshift watercraft down the dirty waters of the canal. The station reports a police helicopter caught up with the riders and ordered them out of the water.