But police believe Brooke Bennett lied about meeting the girlfriend and may have been bound for a meeting with an unknown individual with whom she had communicated through MySpace.com, an online social networking site.
Bennett, of Braintree, was reported missing around 9 p.m. Wednesday, about 12 hours after her uncle and cousin dropped her off at a Cumberland Farms store in Randolph.
She told family members she was going to meet her friend and then go to visit a sick relative of the friend at Dartmouth-Hitchcock Medical Center, in Lebanon, N.H., according to Vermont State Police Capt. David Covell.
"It is the family members' opinion that that was a ruse to the family to get to that location," said Covell. "There's been no interview conducted that supported that that was a legitimate meeting."
Surveillance camera footage from the Cumberland Farms store showed Brooke being dropped off by her uncle and cousin, according to Covell. The footage, which police would not release, showed Brooke walking away from the store by herself, headed toward the village of Randolph, they said.
She hasn't been seen since.
On CBS' The Early ShowBrooke's mother made a heartfelt plea to her 12-year-old daughter who has been missing more than 36
"I'm not mad. I just want you home," she said.
A family member searching for her Thursday in Brookfield - near her uncle's home, where she spent the night - found items belonging to her near Route 65 that were similar to what she had been wearing, prompting an intensive search by police and dogs in the area of the Floating Bridge. Police wouldn't say what the items were.
In the Amber Alert, police said they had no information about a suspect or any vehicle.
Police haven't identified the person she was communicating with, but Vermont State Police computer experts were analyzing the computer in a bid to learn more, authorities said. Police said they don't know if it was a woman or a man.
The girl established her first MySpace account under her father's supervision, but he later pulled the plug on it a couple of months ago after they learned about some of her activity on it, according to the father, James Bennett, 41, of Bethel.
"We told her when we set it up there that's things you're not gonna' do," he said. "We had a little respect problem after a month or so, so we shut it off. There was an issue, and we decided it was not appropriate for her to have it. We changed the password so she couldn't use it," he said.
She later set up an account from another computer, which Bennett said he didn't know until a week ago. The girl lives with her mother in Braintree, not with Bennett.
MySpace.com, the Web's most popular social networking site, has more than 110 million active users. It's a free site, but registration is required.
On Friday, Vermont State Police divers will begin searching Sunset Lake, which is close to the place where the girl's belongings were found. On Thursday, a New England K-9 Search and Rescue dog walked a floating bridge that spans it, under the guidance of handler Nancy Lyons.
Police cordoned off the road that leads to the west side of the lake, and search dogs looked in that vicinity, too, to no avail.
"The floating bridge is a common place for teens to hang out," said Orange County Sheriff Bill Bohnyak. "It's very common for local kids from Randolph, Braintree, Brookfield, Chelsea to come over to the floating bridge."
Capt. Ed Ledo of the Vermont State Police said the Amber Alert wasn't issued earlier because police needed more information. The alert was issued about 5:25 p.m. Thursday, nearly 18 hours after the girl was reported missing.
"Because someone's missing, you can't just put an Amber Alert out. There are certain criteria we're bound by," Ledo said.
About 14 detectives were currently working on the case, he said.
"I'm sitting here waiting for a phone call, hoping it's good news. This is a very difficult time," said James Bennett, her father.
The girl, who just finished seventh grade, is described as 4-foot-11 inches tall, 98 pounds, wearing blue jeans, a pink sweater and white sneakers with pink lettering. She has blue eyes, brown hair with purple highlights and has pierced ears "top and bottom," according to the Amber Alert.
At the Randolph convenience store, a flier with a black-and-white photo of Brooke was taped to the glass door in front, and clerks handed out copies of it to customers inside. A store manager there declined comment on the girl's disappearance.
"It is certainly our hope that Miss Bennett is out there and has just failed for whatever reason to contact family and friends," said Covell. "At this point, we're looking at all possibilities."
Amber Alerts, which are named for Amber Hagerman, a 9-year-old Texas girl slain in 1996, are a partnership between law enforcement agencies, broadcasters, transportation agencies and the wireless industry to alert the public in the most serious child-abduction cases.
Anyone with information about Brooke's whereabouts is asked to call the state police at 802-234-9933.