Three girls living in a South San Jose group home for juvenile offenders attacked and bound their counselor at knifepoint Tuesday morning, then kidnapped another teenager as they fled in a stolen van, police said.

The girls' whereabouts were not known Tuesday night.

An Amber Alert was issued for 14-year-old Enedina Mendez, the abducted girl who also lived at the home, and a 2001 white Dodge van, license plate 4SEV029. The alert was broadcast throughout the Central Valley, though police would not specify why the areas around Tracy, Stockton and Modesto were targeted. None of the girls sought Tuesday is from Santa Clara County.

A woman who identified herself as a counselor at the home at 1457 Kooser Road, just north of Blossom Hill Road, told police that three of the residents -- a 17-year-old and two 15-year-old girls -- threatened her with a kitchen knife and tied her up near the garage. They then grabbed the keys to the group home's van, along with more than $100 cash from her pockets.

The counselor, whose name was withheld Tuesday and who declined to be interviewed, said she heard a brief commotion as the teenagers prepared to leave. Mendez had just arrived home.

``The counselor said she heard the girl say, `No, no. I don't want to go,' '' said police official Gina Tepoorten. ``We do believe they forced her to go with them.''

Police initially searched for another van, which turned up about 5 p.m. some 10 miles from the home. But none of the missing girls was inside, and police quickly revised the description of the suspects' vehicle. It remained unclear what led to the discrepancy.

Neighbors on Kooser Road cautiously approached investigators past rows of patrol cars to find out what had happened on their otherwise quiet tree-lined street.

Diane Guzman grabbed her stomach in disbelief at news of the incident, but was more troubled that such a home was just a few doors from her house.

``I'm all for helping troubled kids, but I'd like to be informed that this home is right here,'' she said, glancing at the single-story, cottage-ranch home. ``So, this is the place where they can just dump their troubled youth? I'm in shock.''

Other longtime neighbors said they knew the cream-color house with the brown trim was a group home and never had a problem with the residents.

``They would always say, `Hi,' '' said Elaine Ellis, who passes the home each day on her way to work near Princeton Plaza, across the street. ``I never heard of trouble at the home.''

Police said the group home opened a year and a half ago to house teenage girls from across the state who had violated their probation. Tepoorten could not discuss what offenses landed the suspects and Mendez at the home, or whether they had violent histories. She also could not say how long the girls had lived there.

The facility is run by EE Residential Group Homes, a state-licensed provider. Several calls to the agency were not returned, and a woman later reached by phone declined to comment.

Police continued to search late Tuesday for the four girls. One of the suspects was identified as 17-year-old Jasmine Jones, an African-American girl last seen wearing a gray shirt and blue jeans. The two other suspects were described as a 15-year-old Latina with short dark hair, also wearing a gray shirt and blue jeans, and a 15-year-old Asian-American girl who had her dark hair in a ponytail.

Mendez is described as a 5-foot-6 Latina, weighing 145 pounds with brown hair, brown eyes and last seen wearing a gray sweat shirt, with her hair in small ponytails on top of her head.

Anyone with information can call Lt. Mike Sterner at (408) 277-4166. Those wishing to remain anonymous can call (408) 947-STOP.