Abigail was last seen Oct. 9 leaving Kennett High School about 2:30 p.m.
The vigil was held Sunday from 6 p.m. to 10 p.m., with organizers asking participants to post about Abigail on Facebook and Twitter using the hashtag "bringabbyhome," the Boston Globe reported.
Participants also changed their Facebook profile pictures to one of a set of images of Abigail.
The FBI has offered a $20,000 reward for information leading to the conviction of anyone involved in the teen's disappearance.
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