I did not find a William Pepper on my list of Indian Captives released to Col. Bouquet at Ft Pitt 1764-1765....but many of the children had been taken when so young, they only knew their Indian names and are listed that way.Others are listed such as: girl with sore knee....
I got the copy of the list from: Historical Society of Western Pennsylvania Library and Archives Division 1212 Smallman Street Pittsburgh, PA15222-4200 it only cost me $6.50 and I got it in the mail in 2 days.I would imagine a lot of other information would be found there.I have also been told a lot of the Virginia captives, there is information at the Eastern Tennessee Hist. Society - I think that is in Knoxville.
Many captives names were written in the PA papers after their release, but not sure where you would find that.If you find out, let me know as I am looking for any information on surname Turney taken in Virginia or western PA.There are conflicting stories - one that Henry Turney was taken, he would have been living on the North Branch of Shenandoah River between Woodstock and Edinburg, VA....not far from his home the Painter family was taken. There is a boy named Henry listed as released, but no last name.... The other story is about a John Turney - probably from western PA....and on the list of released captives there is a "Dutch John".Since the Turneys were German speaking Swiss, either or both could be possible....some of the Turneys stayed in PA and moved to Hannastown near Greenburg PA area, not far from Ft Pitt.
There are a couple of discussion boards on Indian captives if you are interested, let me know.
A lot of old books were written (now of course out of print) which mention local raids and who was taken.People are finding these and trying to collect all the names.
I have not found the Pepper name in my research, but will keep you in mind.
Try to find old county history books, they might mention the raid and have more information for you.Exactly which county/area are you looking at? Of course, what it was back then would be very different from what it is today.That just makes it more difficult trying to find information about those early settlers.
You might also look at the Pepper genforum page, there might also be one on ancestry.com surname board.