"I think by now he's hungry, tired and looking for a familiar face to connect with," said volunteer Kimberly Sorrell, a volunteer.
Kyrin was last seen Saturday afternoon, when he left a hotel room at the Best Western in the 3800-block of 179th Street, where he was staying with his family. They were here for a weekend visit from Kansas City.
A camera in the back of the hotel captured an image of Carter as he left.
It appears Kyrin, who is nonverbal but highly functional, was wearing blue shorts with possibly blue or white stripes, a blue t-shirt, but was not wearing socks or shoes, police said.
Dogs apparently picked up a scent near the river behind the hotel, and search crews have concentrated their efforts here.
The case has attracted numerous volunteers anxious to help.
"I have a special needs brother and this touched my heart. We need to bring him back to his family," said volunteer Mike Jankovich.
Family members said they are grateful for the help. Many are too emotional to talk about it at this point, they are just hoping to find Kyrin.
"If' ya'll seen my nephew. Bring my nephew home," said his Aunt, Keisha.
Search crews have been looking underwater, by boat, on land.
Over the weekend a chopper flew overhead and Tuesday afternoon a drone flew over the area.
"It's a sad story. Hopefully we get a happy ending out of it," said Jankovich.
Anyone with information is asked to call 911.