The Egyptian men were kidnapped by IS as they tried to flee the Libyan capital Tripoli in August.
Relatives have made the plea just days after 21 Egyptian Copts were beheaded by IS after they were also abducted in Libya.
All of the men, brothers Jamal Matta Hakim, Ra'if Matta Hakim, Rumana Matta Hakim and their cousin Adel Siddiq Hakim, left the southern Egyptian city of Abu Teeg to find work in Libya.
It's thought they were separated from Muslim men at a check point when they were taken.
Family members are now appealing to the Egyptian and Libyan government for help to negotiate their release.
Egypt has already bombed several IS sites in Libya since a video emerged showing 21 Copts being beheaded at the hands of IS.