Plain missing / Emma Miller.

Enhanced descriptions from Syndetics:

Inn owner Rachel Mast is no longer a devout member of the Amish community of Stone Mill, Pennsylvania, but she still cares deeply for them. So she's staying at her family's farm to help her mother through an illness--and at the same time, trying to track down two missing people . . .

When the young gather to sing, it's usually an evening of wholesome fun--but this time, the event has stirred whispers of scandal. Elsie Hostetler and her sweetheart, Dathan Bender, never came home afterward. There's not even a trace of their horse and wagon, leading some to suspect that they've run off to marry and join the Englisch world.

But Rachel fears there's more to the story than a rebellious elopement. Her fiancé, a state trooper, is out of town, so she starts investigating herself, using her Amish background to pry information from the tight-lipped community. It turns out things were not so peaceful between Elsie and Dathan--and there was also a confrontation at the singing with a short-tempered ex-Marine. Among the simple houses and quiet country roads of Stone Mill, Rachel must find out just what kind of sins have been committed--and who is need of forgiveness . . .

Praise for the Amish Mystery series

"An excellent addition to the Amish mystery subgenre."-- Library Journal

"An exciting tale of mystery, love, and danger."-- Booklist

"A well-informed look into the tranquil world of the Amish with a fairly edgy puzzler."-- Kirkus Reviews