FORT COLLINS, Colo. -- What happened to a 16-year-old Fort Collins girl when she disappeared for a few hours last Friday night? That's what has police officers and the girl's family stumped.

An Amber Alert was issued Saturday at 2 a.m. after Brooke Norris' friends called police to report that she was missing. Norris' friends said that she had left their home in the 3200 block of Fernwood Lane around 10:40 p.m. But an hour later, when they went outside, they saw that her car was still in the driveway and her keys and one flip-flop were on the ground.

Nearly six hours later Norris ran into her family home in the 2900 block of Southmoor Drive in southeast Fort Collins, relatively safe and sound. She said she woke up at 6 a.m. in the green belt area, behind 3300 Creekstone Drive, with a bump on her head but she doesn't know how she got it, Fort Collins police said.

Detectives have been working with the teen to determine her whereabouts but they're left with few clues and are asking for the public's help.

Norris said she doesn't remember much from that night. She said outside her friends' home, she saw a teenage boy who chased her down the street. She also remembers seeing an older model two-door pickup truck with a silver stripe down the side with possibly two people inside. However, she doesn't know if the truck was associated with the teen who chased her.

The other teen is described as approximately 15 years old with short dark hair and a "chunky" build. He also had an earring in his left ear.

Police do not believe Norris was taking any drugs or alcohol.

Police are asking anyone who has any information about this incident or who may recognize the teen boy to contact Fort Collins police at 970-221-6582.