During her first week of summer vacation, a shy 13-year-old girl took her new dog out for a walk one evening about an hour before sunset. Christina Williams never returned.

Her parents say she was not the kind of girl to run away. Her money was still in her room when she disappeared June 12, and she would not have left her new dog, Greg, behind.The FBI believes Christina was abducted but refuses to speculate about what happened afterward.

Since their daughter disappeared from this nearly vacant former military base where they live, Christina's parents have spent their days trying to get her back.

They distribute fliers with Christina's picture and sketches of two suspects, have made more than 10,000 badges bearing their daughter's picture and have answered thousands of e-mails offering support.

"Christina. One word," says her father, Navy Chief Petty Officer Michael Williams Sr. "For the most part, everything revolves around Christina. Doing something to try to get Christina back."

It was November when the Williams family moved from Japan to the now-closed base about 130 miles south of San Francisco. Formerly the West Coast's largest training command, the 28,000-acre expanse of rugged terrain has thousands of boarded-up buildings and is home to just several hundred military families.

"Everything is vacant," said Christina's 18-year-old sister, Jennifer. "It's not like the normal community where you're in this closed, safe area. It's unlike any other base we've been at."

The Williams family got some quick help from Mark Klaas, who formed a missing child-response team after the kidnapping death of his daughter Polly in Petaluma.

Oakland Raiders running back Napolean Kaufman taped a public service announcement Tuesday for Christina, who was wearing a Raiders shirt when she disappeared. Earlier, Clint Eastwood, Reggie Jackson and Mariah Carey made televised pleas, and her parents appeared on "Larry King Live."

A fund for information leading to her return holds more than $100,000, and her picture and the suspect sketches are on storefronts from California to upstate New York.

Her story also has been featured twice on "America's Most Wanted," which prompted two recent sightings in Greensboro, N.C., of a girl witnesses believed to be Christina.

"There have been other sightings about 10 times of someone who resembles Christina and that turns out negative," Williams says. "Are we hopeful? Yes. But we temper that knowing there have been other sightings and those have not panned out."

On June 12, a jogger on the base was harassed by two men in a car believed to be the one Christina was later spotted in by a witness who said she saw a frightened 13-year-old girl.

On the night she vanished, Christina's father was in the honor guard for President Clinton's visit to nearby Monterey. With the president's trip and the National Basketball Association finals on television, the streets on the base were more desolate than ever.

"If Christina had screamed, no one would have heard it," Williams says.

For Alice Williams, the most difficult thing is the uncertainty about her daughter.

"I think she's alive and someone is hiding her or taking care of her," she says in the family's living room, which is filled with cards of encouragement. "I don't think she's hurt or something. I think she's OK."