Writing on Twitter for the first time in a week, Hariri assured his followers that he is okay and that he would return without his family, who the prime minister said will be staying 'in their home' in Saudi Arabia.
Government officials in Beirut have said they believe Hariri is being held in Saudi Arabia, amid a deepening crisis pushing Lebanon onto the front lines of a power struggle between Saudi Arabia and Iran.
Lebanese President Michel Aoun has refused to accept Hariri's resignation, which came under mysterious circumstances, until Hariri returns to Lebanon.
Saudi Arabia supported Hariri and his allies during years of political conflict in Lebanon with Iran-backed Hezbollah.
In his resignation speech televised from Saudi Arabia, Hariri denounced Iran and Hezbollah for sowing friction in Arab states and said he feared assassination. His father, former Prime Minister Rafic Hariri, was killed in a 2005 bombing.