"The opposition is beginning active pursuit of the president," Eka Beseliya, leader of the For a United Georgia movement, told a rally, inviting supporters to report on the president's whereabouts for protesters to be able to block his motorcade.
The appeal came after Saakashvili made another attempt earlier on Thursday to persuade the opposition to end street protests and join efforts to tackle the economic crisis.
"I am prepared to cooperate with all the political forces, including the most radical of them. Georgia now needs our unity, not conflicts," he told workers at a factory near Tbilisi, pledging to iron out political differences and create jobs in the ex-Soviet Caucasus state, which has been hard-hit by the global financial crisis.
Twelve members of the ruling National Movement party's provincial branch joined the protests on Thursday, to the cheers of thousands of opposition supporters rallying in front of the parliament building. Opposition leaders described the move as "a hope-inspiring signal."
Opposition leader and former parliament speaker Nino Burdzhanadze urged other ruling party members "to join the nation before it is too late."
The opposition started the protests on April 9, and has vowed to keep them going until Saakashvili steps down.
Saakashvili, a U.S.-educated lawyer who came to power on the back of 2003 street protests, has been criticized for undemocratic policies and for dragging the country into a war with Russia last August, which resulted in the permanent loss of two separatist provinces.
Tens of thousands of opposition supporters gathered in the capital, Tbilisi, on the first day of the protests. Several thousand protesters remain gathered in the city center every day, with activists picketing the presidential residence day and night.
The opposition has built wooden jail cells on Tbilisi's central street to symbolize the country's descent into a police state, and thousands of new supporters arrived in the capital from provinces late on Wednesday. Police have not attempted to disperse the rallies.
