ARVADA, Colo. (CBS4) – A military helicopter on Sunday helped look for an Arvada teenager missing for two days. Police are now intensifying their search.

Christine Harvey was last seen Friday afternoon at about 4:30 p.m. She’s 19 but has the mental capacity of a 12-year-old.

Harvey was spotted at a Valero convenience store across from Lakeside Amusement Park on Sheridan Boulevard. She lives near the 6200 block of Wolff Street and in order to get to the convenience store she would have had to walk more than 20 blocks. That would have included getting past two interstate highways and a series of railroad tracks.

Police released surveillance images of Harvey inside the convenience store. They were taken a little over an hour after she disappeared on Friday. Police believe Harvey is alone.

Police used the military helicopter to search areas that might have been difficult for Harvey to walk. They also searched trails in the area and Sloan’s Lake. A reverse 911 call went sent out Sunday morning in the Arvada area where she disappeared. A volunteer search team is still active.

Christine Harvey (credit: Arvada Police Department)

Arvada police received two new tips about Harvey’s disappearance Saturday night and Sunday morning. In both reports witnesses say Harvey asked for directions to a Jefferson County library. Now police are searching every library in the area, including Wheat Ridge, Arvada, Denver and Edgewater.

“The concern that we had originally, and still do, is that she’s quite shy. So we were worried that she wouldn’t go ask for help or tell people that she was lost,” Sgt. Michelle Moriarty with Arvada police said.

Harvey at the Valero convenience store across from Lakeside Amusement Park on Sheridan Boulevard on Friday (credit: Arvada Police Department)

Harvey was last seen wearing black pants and a blue top. She has long, blonde hair and wears braces on her teeth.

Harvey’s family says they are growing more concerned with every passing hour.