Question: Which of the ancient prophets named in the Book of Mormon are not named in the Old Testament? Were two of them ancestors of the Nephites?
Answer: There are four ancient prophets named in the Book of Mormon, who are not mentioned by name in the Bible---Zenos, Zenock, Neum, and Ezias.
Zenos is mentioned twelve times, Zenock five times, and Neum and Ezias are each named once.
One verse seems to indicate that the Nephites were descendants of Zenos and Zenock, for it says of them, “Yes, the prophet Zenos did testify of these things, and also Zenock spake concerning these things, because they testified particularly concerning us, who are the remnant of their seed” (3 Nephi 10:16).
Source: 400 Questions and Answers About the Book of Mormon by Susan Easton Black, p. 170.