Police say Teresa Cathy Mastracola of Millbourne Avenue in Millbourne, Pa. has not reported to work for several days.
She is described as 44 years old, 5'7" tall, 130 pounds with brown eyes. She was last seen wearing hospital scrubs.
Her co-workers became concerned when she failed to show up for her job as an Imaging Equipment Specialist at Delaware County Memorial Hospital this week.
Mastracola is described as a truly beloved member of her community.
Neighbors say she would routinely host parties for other people's children, even though Mastracola had no children of her own.
"She's pretty much a people person out here every day playing with all the children on the block," said Erica Harrison.
"She's really sweet. Everybody, every kid liked Theresa," said Shahdan Hossein.
The last person to see Mastracola was her roommate. He says she left their house between 9:00 a.m. and 10:00 a.m. Sunday morning.
Police say she drives a silver 2006 Mazda 6 4-door sedan with a black bicycle rack and Pennsylvania license plates DTA-5563.
At this point, police are reluctant to call Mastracola's disappearance suspicious because she is an avid hiker who often leaves town for days.
"We are trying to figure out if she went out of state or if she turned her phone off and just didn't want to talk to anyone. We're looking into airlines, to see if maybe she bought a ticket and took a plane ride somewhere," said Chief Shawn Payne.
The fact that she hasn't checked in at work or returned calls from her roommate or family is raising concern.
They say her phone was on until about 9:00 p.m. Wednesday night, but now it is either off or has died.
"It's kind of concerning why she is not contacting anyone. Even if she wasn't making it to work, why is she not contacting her employer? She is a reliable employee," said Chief Payne.
Both the Delaware County District Attorney's office and the Criminal Investigation Department are now involved in the case.
Anyone with information on Mastracola's whereabouts is asked to call Millbourne Police at 610-352-1450 or 911.