From the unpublished manuscript, Indian Atrocities Along the Clinch, Powell and Holston Rivers, page 32.
John Redd who came to Martin's Station in Powell Valley in 1775, from Henry County with Captain Joseph Martin, tells the following story in his narrative: (1)
In the spring of 1775, a man by the name of Jacob Lewis came out to Martin's Station in Powell Valley, with a wife and seven children. Some of the men knew him to be a man of bad character and he was ordered not to settle near the Station. Lewis took his family and came in the direction of the settlement, about thirty-five miles, and built him a small cabin near the head of Stock Creek, and there lived entirely on the game he killed. In June, 1776, when on my way to the settlement, (on Clinch) I passed by his house and advised him to move to the settlement that the Indians had declared war. He said he was in no danger; that the Indians would never find him. In July, following, as I returned to the Holston, I learned that Lewis and wife, and seven children were killed and scalped by the Indians.
Other than Redd's story I have been unable to find any confirming evidence of the massacre of the Lewis family. The records of Washington County, VA, show that Jacob Lewis did have a grant for 400 acres of land in Powell Valley on Wallens Creek, surveyed for him on August 14, 1781, (posthumously if he was killed in 1776), and shows a settlement date of 1776.
(1) John Redd's Narrative, Vol. 6 & 7, Virginia Magazine of History and Biography.