Police have said the 49-year-old neighbor, David Westerfield, is a potential suspect and they have searched his San Diego home several times.
Near the sites where Westerfield might have camped, volunteers found a Winnie-the-Pooh mylar party balloon, a page torn from a "Lion King" coloring book and a Charms "Sour Apple" lollipop wrapper, among hundreds of other items.
On that outside chance that one of the items could be traced to Westerfield or Danielle, Vicki Warren of the ASA collected all of the items brought in by volunteers so that investigators hired by the Laura Recovery Center could sift through the collection later to check for clues.
The recovery center was founded in 1997 to help coordinate a search for 12-year-old Laura Smither of Friendswood Texas, a suburb of Houston.
Laura's body was found after a 17-day search.
In the years since, the center has helped fund searches for missing children.
Warren said if volunteers found an item that was too big to carry back from the dunes, volunteers with Global Satellite Positioning systems could mark the site and the item would be inspected later.
The majority of the volunteers began searching at 11 a.m. methodically examining campsites near washes 13, 14 and 15 west of Ted Kipf Road just south of the Glamis Store.
Janice Jackson of Corona couldn't wait for the others, though.
Just after 10 a.m., she walked with a San Diego woman near the spot where Westerfield is reported to have gotten his RV stuck in the sand on Feb. 3.
Jackson, a mother of three, said she was hoping to help give the van Dam family closure.
"I know I would want someone to help look for my daughter.
"It really hits home. It's a wake-up call to middle-class America," she said.
Jackson arrived in Glamis on Friday night.
"We planned out last night where to look. Today I have been thinking, ‘What would be his next move?'"
According to the San Diego Union-Tribune, Westerfield's neighbors described him as smart and confident with an immaculate house and a fondness for dune buggies and camping in the desert. He owns a company called Spectrum Design.
Westerfield's RV and Toyota Forerunner have been searched by San Diego police.
Francesca Williams, who accompanied Jackson on Saturday morning, searched the Rancho San Diego area on Friday and drove to Glamis to volunteer there the next day.
Asked why it was important for her to join the search, she said, "This could be anyone's little girl."
Back at the ASA hub, Warren talked about why her off-roading group is perfect for such a mission.
"A lot of people don't know what they are looking for. We know the desert and we love it," she said.
Before sending the volunteers out at 11 a.m. Warren briefed everyone on what they should be looking for.
She said Danielle was last seen wearing blue pajamas.
At 3 p.m., Damon van Dam arrived at the ASA gathering place near Wash 15 to rally the volunteers and ask them to search again starting at 9 a.m. today.
On Friday, Danielle's mother, Brenda van Dam, released a videotape of her daughter, set to music, in hopes of drawing further help to the search effort.
‘‘I hope, I hope that someone will tell where she is," Brenda van Dam said. ‘‘You could only hope.''
Calexico Firefighter Art Navarro said he searched for Danielle on Saturday because, "We all have kids of our own."
He added: "I'm here because I heard they need people to help."
While the off-roaders look for clues again today in Glamis, volunteer search parties are scouring the San Diego Aqueduct in Poway, miles away from the van Dam residence, according to the San Diego County Sheriff's Department Search and Rescue Team.
>> The Associated Press contributed to this story.
>> Staff Writer Aaron Claverie can be reached at 337-3419 or firstname.lastname@example.org