The Ansar al-Sharia militia kidnapped 13 of them Saturday in the coastal city of Sirte and the rest of them there over the past few days, the source said.
Their identity was not immediately clear, except that they were said to be Coptic Christians.
Thousands of Egyptians work in Libya, mainly in the construction and craft sectors, and they have been targeted as the country has descended into chaos.
In February, the bodies of seven Egyptian Christians who had been shot were found near the second city of Benghazi.
And just last week, an Egyptian Coptic couple were found dead in their home in Sirte, hometown of longtime dictator Moamer Kadhafi, who was overthrown and killed in a NATO-backed uprising three years ago.
Their 13-year-old daughter, who was kidnapped, was later found dead.
Local council chairman Yussef Tebeiqa said the attack might have been motivated by religion as money and jewellery were not taken.
Since Kadhafi's ouster, Libya's small Christian minority has expressed fears over Islamic extremism, especially with the rise of armed militias enforcing their own law in the absence of central control.
Sirte, 500 kilometres (310 miles) east of Tripoli, is in the hands of Islamist militias, including Ansar al-Sharia, which the UN last month added to its terror list over links to Al-Qaeda and for running Islamic State group training camps.
UN talks start Monday
Libya is awash with weapons and powerful militias, and has rival governments and parliaments.
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French Defence Minister Jean-Yves Le Drian recently called on the international community to act to prevent Libya from becoming a "sanctuary for terrorists".
As well as Sirte, Tripoli and second city Benghazi are largely in the hands of militias, and the internationally recognised government has taken refuge in the remote east.
Benghazi residents said they have been suffering from shortages of electricity, water and fuel since Wednesday.
Last week, the army led its first air raids on Islamist positions in Misrata, an important base for fighters from the Islamist-led Fajr Libya (Libya Dawn) coalition of militias.
On Saturday, Libya's third city was once again hit by aerial attacks, according to military sources, who did not give any casualty figures.
Separately Saturday, Islamist fighters attacked and killed 15 soldiers in the town of Soknah, 180 kilometres southeast of Tripoli, a source close to the government said.
Some of the troops were shot dead and others decapitated by militants who have pledged allegiance to IS, the source added.
UN-brokered talks aimed at ending months of violence and political deadlock in the North African nation are scheduled to begin on Monday.
A UN diplomat said the initiative calls for a ceasefire as well as a withdrawal of all militias and the disarmament of the warring sides.
Libya's internationally recognised parliament has voted not to attend the negotiations if the rival legislature in Tripoli is party to the talks.
Last month, leaders in the sub-Saharan Sahel region of Africa meeting in Mauritania called on the United Nations to organise an international force "to neutralise the armed groups" in Libya.
Libya's violence has drawn strong condemnation from both the UN and European Union, and rights group Amnesty International has accused several factions of war crimes.