Julia Campbell was last seen on April 8 in the town of Banaue in Ifugao province, where she had planned to hike alone, said U.S. Embassy spokesman Matthew Lussenhop.
Campbell, 40, wrote for the New York Times and other publications in the past. She also worked for a time editing news and features for Courttv.com, Court TV's Web site.
She was involved in a controversial March 1997 case. Covering the funeral of the rapper known as Notorious B.I.G. in Brooklyn for the Times as a freelancer, she was arrested by police for disorderly conduct -- she allegedly tried to incite attendees -- but later cleared.
She charged that the police had pepper sprayed her in the encounter and the Times argued that her press credentials were clearly displayed.
Campbell went missing in an area about 160 miles north of Manila that is famed for its mountainside rice terraces and pine forests. The armed wing of the Communist Party -- the New People's Army -- also operates there.
In 1990, the New People's Army seized Peace Corps volunteer Timothy Swanson and held him for 50 days on central Negros island. He was released unharmed to the Red Cross.
Lussenhop said the Peace Corps started looking for Campbell after she missed appointments on April 11.
"Embassy security officials and Peace Corps security and local authorities are in that region right now looking for her or finding people who may know where she is," he said.
Regional police commander Chief Superintendent Raul Gonzales said at least four teams from the provincial police office have been mobilized for the search, after the U.S. Embassy told them Campbell was missing.
He said the directive to conduct the search came from the national police headquarters in Manila.
Maj. Gen. Rodrigo Maclang said members of an army company in Banaue also joined the search Saturday, after receiving an order from the military's Northern Luzon Command.
A military helicopter will help with the search, he said.
"We were unaware of the incident. We learned only today that someone has been missing," he said.
Maclang said there is only a small military presence in area because "it is not a major concern now with regard to the insurgency."
As early as Thursday, local police started checking the guest registries in hotels and inns for Campbell's name, receptionist Lea Ananayo at the Halfway Lodge in Banaue said by telephone.
Authorities also left Campbell's photos to be displayed in hotel lobbies, shops and market stalls in the town.
Campbell, of Fairfax, Va., has been teaching college in Albay province's Legazpi city, southeast of Manila, since March 2005.
She was planning to hike in a hilly area near Batad village, about a mile east of Banaue's town center, the embassy said.
The embassy appealed to the public for any information on the welfare and whereabouts of Campbell. It offered a reward, but did not specify an amount.
Campbell, who worked as a journalist in New York, contributed a story to CNN about the death and destruction in the wake of supertyphoon Durian, which hit Legazpi in late November.
Writing in her Internet blog, she said she "decided to step out of the rat race of New York" to join the Peace Corps when she was 38.
In an entry on May 27, 2005, two months after her arrival in the Philippines, she expressed anticipation about no longer having "the comfort of fellow Americans within reach."
"I will be left to my own devices in a strange place with people and a culture I barely know," she wrote.
Campbell is one of 137 Peace Corps volunteers currently in the Philippines.
More than 8,000 Peace Corps volunteers have served in the Philippines since 1961, making it the corps' second-oldest program in the world, the embassy said.
A New York Times account on April 12, 1997, included the following.
At the request of the Police Department, the Brooklyn District Attorney yesterday dismissed a disorderly conduct charge against a freelance reporter who was arrested last month while covering the funeral procession of the slain rapper Christopher G. Wallace for The New York Times.
Calling the arrest unfortunate, Police Commissioner Howard Safir announced the decision to seek dismissal of the charge yesterday, saying in a news release that ''pursuing charges would be counterproductive to the Police Department's goal of fostering good relations between the police and members of the press, and its understanding of the public's right to know about the activities of police officers, particularly at scenes of public demonstrations.''
The reporter, Julia Campbell, was arrested on March 18 during a scuffle between police officers and rap fans in Fort Greene, near the family home of Mr. Wallace, who recorded under the names Biggie Smalls and the Notorious B.I.G. At the time, she was wearing a Police Department press pass issued to The Times.
The news release also said, ''Both the Police Department and The New York Times agreed that the arrest could have been avoided with a greater degree of insight and respect by both the police officers and the reporter for their respective roles in attempting to do their jobs under difficult and dangerous circumstances.''
According to the release, Mr. Safir's characterization of the arrest as unfortunate was accompanied by an acknowledgment from Michael Oreskes, metropolitan editor of The Times, that Ms. Campbell's use of harsh language in the heat of the moment was ''not appropriate.'' The two men pledged to work toward a better understanding between officers and reporters.
The New York Press Club, which has said there is a pattern of police mistreatment of reporters and photographers at news events, said it was happy that the charges had been dropped.
The Press Club statement added: ''We are still mystified by the details placed in the police report about Ms. Campbell exhorting the crowd to disobey the police and pushing an officer. Clearly, the Commissioner says he intends to do better in the future. We applaud his resolve to improve relations with the press. But the proof of this will be in what happens when reporters and photographers try to cover stories.''
By: E&P Staff and The Associated Press The Philippine police and military are searching for a U.S. Peace Corps volunteer missing for nearly a week in a mountainous northern area, officials said Saturday.