The workers include a 39-year-old Austrian from Linz, a Czech national, and seven people from Bangladesh and the Philippines. They went missing after a militant attack on a Libyan oil field, in which eight guards were killed.
No demands have been made by any group or individual for their return.
Senior Austrian ministry official Michael Linhart blamed the attack on Islamic State-allied militants from nearby Sirte, who "are known to have been behind the brutal execution of a group of Coptic Christians in the past."
The missing Austrian was named in unconfirmed Austrian media reports as Dalibor S., a father-of-two oil manager and former soldier.
Linhart told the Austria Press Agency on Sunday that "there is currently no sign of life nor proof of death" from the workers. He added that Austria is in contact with Libyan authorities.
Philippines foreign department spokesman Charles Jose said Manila's embassy in Tripoli had reported that four Filipinos and five foreigners had been snatched, including the Austrian, two Bangladeshis, a Czech national and a Ghanian.
The attack "underscore[s] the escalating threat to the safety and security of Filipino oil workers in Libyan oil fields which have been targeted by armed groups in recent weeks," Jose told a news conference, adding that no demands had been issued.
VAOS, an Austrian company that offers construction services to oil companies, had evacuated dozens of other workers to the Libyan capital before the attack.