"Although positive identification has not been made, there is (a) strong likelihood that we have found Chelsea," he told reporters.
Gore said he had informed the teen's parents.
"Obviously they are devastated and I ask that you respect their privacy during this extremely difficult time," he said.
Hours later, several thousand people holding candles and tearfully embracing joined the teen's parents, Brent and Kelly King, in a vigil outside St. Michael Catholic Church in suburban Poway.
Brent King spoke briefly, thanking everyone for their efforts to find his daughter.
"One of the nicknames that I've always called my daughter is my Angel. She's my angel forever," he said.
"I want to thank you. Chelsea wants to thank you," he said.
When someone shouted, "We love you," Brent King responded, "We love all of you."
Police, meanwhile, said the registered sex offender suspected in King's disappearance likely assaulted a jogger in December in the same park.
The 22-year-old Colorado woman managed to fend off her attacker on Dec. 27 in Rancho Bernardo Community Park on the northern edge of San Diego, where King's 1994 BMW was found with her belongings inside, police Capt. Jim Collins said.
Police said evidence has linked 30-year-old John Albert Gardner III to both cases but further details have not been released.
Collins, however, said a swab taken from the elbow of the Colorado woman did not match Gardner's DNA.
Gardner is now in custody without bail for investigation of murder and rape in the King case.
Gardner of Lake Elsinore pleaded guilty in May 2000 to molesting a 13-year-old female neighbor. Prosecutors said he lured the victim to his home with an offer to watch "Patch Adams," a 1998 movie starring Robin Williams
The girl was beaten before escaping and running to a neighbor.
Gardner served five years in prison after prosecutors rejected a psychiatrist's advice to seek stiffer punishment, court documents state.
Prosecutors said in 2000 that Gardner's lack of a significant prior criminal record justified less than the maximum sentence. They also said they wanted to "spare the victim the trauma of testifying."
Gardner had faced a maximum of nearly 11 years in prison under terms of his plea agreement. Prosecutors urged six years -- the sentence later ordered by a judge.
In their 11-page sentencing memo, prosecutors said Gardner "never expressed one scintilla of remorse for his attack upon the victim" despite overwhelming evidence.
Psychiatrist Dr. Matthew Carroll wrote in sentencing documents, "There is no known treatment for an individual that sexually assaults girls and does not admit to it in any way."
Paul Pfingst, the San Diego County district attorney in 2000, said he had no memory of the case but added a six-year sentence was not unusual for someone with no significant prior criminal record.
The district attorney's office declined to comment or make available David Hendren, the prosecutor who handled the case.
State records showed Gardner was released from prison on Sept. 26, 2005 and was on parole for three years.
Chelsea King was described as a straight-A student at Poway High School, playing French horn for the San Diego Youth Symphony, competing on her school cross-country team and volunteering in a peer counseling program.
In an interview Monday with The Associated Press, the Kings, who also have a 13-year-old son, recounted learning Thursday that their daughter had disappeared.
Brent King had returned from the gym around 5:30 p.m., the same time his wife, Kelly, 48, got home with groceries. Chelsea, who always kept them advised of her whereabouts, wasn't home.
"Because it was so out of character for Chelsea not to tell us or call us and say I'm going to be late ... we just had that feeling," Brent King said.