Police said Sharp was last seen Nov. 9 but wasn't reported missing until Nov. 17. They said she last logged into her MySpace page on Nov. 14.
Rios was last seen going to the Campos home Nov. 15 to watch a football game, Evans said. The fragmented remains were found in a makeshift backyard grave outside the home, which the Campos family had been renting for the past two months, he added.
"The only thing I know is my son, he never (would) stay and not talk to me for a long time," said Rios' mother, Elodia Lopez.
Evans said the none of the teens had a history of running away.
Remains found in the backyard on Nov. 18 were later identified as human and a second search Wednesday turned up more bones, which Evans said were in small pieces that may take weeks of examination to identify.
Because of their condition, Evans said he could not immediately link the remains to either of the missing teenagers.
"I can't tell you if it's one person, two people, a male, a female," he said.
Neighbors reported smelling smoke from what appeared to be a bonfire or barbecue at the home last weekend.
Matt Miller, 21, who lives two houses away, said two teenagers matching the description of the missing boys ran onto his lawn in a panic at about 6 p.m. Sunday. Their eyes were red and swollen.
The teens told him that they had been in a fight and claimed that someone had pepper-sprayed them. They also said police were after them.
Miller washed their eyes with milk and they ran off, he said. Several hours later, he and his wife smelled a foul burning odor.
"It was a very strong smell. I've never smelled it before," said his wife, Irene Miller. "We had to shut our windows, it was so bad."
A large swath of the block was cordoned off with police tape Wednesday as a dozen neighbors gathered around the single-story stucco house where investigators brought out bagged evidence and loaded them into trucks. The driveway was cluttered with household items such as boxes and bags of clothes.
Lopez said she was convinced her son is still alive.
"I feel it in my heart," she said.