Brittany Thompson
Brittany Thompson was last seen at the library Monday in Medfield, Massachusetts. Massachusetts State Police

Brittany Thompson, a 17-year-old developmentally disabled girl who disappeared Monday, is believed to be “endangered,” say the Massachusetts State Police.

Brittany was last seen leaving the library in Medfield around 4:25 p.m. Monday, accompanied by a white man described as heavy-set with slicked-back hair and wearing a “Sons of Anarchy” T-shirt, the State Police said on its Facebook page Wednesday. The force also distributed a photo of the suspect:

This man was seen leaving with Brittany Thompson from the library in Medfield, Massachusetts. Massachusetts State Police

“We have reason to believe Brittany Thompson is endangered,” the message read, urging anyone with knowledge of Brittany’s disappearance to call the State Police at (508) 820-2121. Authorities did not indicate why they believe so.

Brittany, who is developmentally disabled, was last seen wearing a red sleeveless shirt, blue jeans and flip flops. She has braces, typically wears sunglasses on her head and is described as being about 5-feet 6-inches tall and weighing 140 pounds.