The controversial scheme is aimed at beating the country's powerful illegal armed groups.
On a visit to the north-eastern state of Cesar, Mr Uribe set up the first group of informers - 600 unarmed volunteers who will work alongside the police and army.
Colombia has been plagued by civil war for decades and the new leader's inauguration was marked by a wave of bomb blasts in the capital, Bogota.
Concern
The BBC's Jeremy McDermott says that the new informer network - billed during the election campaign as a "million-man militia" - is particularly aimed at establishing authority in the half of the country currently under the domination of Marxist guerrillas, right-wing paramilitaries and drug barons.
But human rights groups have already expressed concern over the plan, arguing that it will drag more civilians into the civil war.
The proposed informer groups also risk evolving into new paramilitary groups.
Our correspondent says that Mr Uribe threw himself into his new job on Thursday, travelling around the country amid huge security, seemingly undaunted by Wednesday's bomb attacks.
"We call on all Colombians to cooperate with the armed forces with the aim of defeating the violent minority," said Mr Uribe, speaking in the city of Valledupar.
Cool performance
The death toll in an attack on the presidential palace has climbed to 17 and more than 60 people were wounded.
Someone to spy on: Colombia's groups
Revolutionary Armed Forces of Colombia (FARC) - the biggest Marxist group
National Liberation Army (ELN) - FARC's leftist rival
Self-Defence Forces of Colombia (AUC) - rightwing paramilitaries
On radio stations across the country, people were asking how President Uribe would be able to reconquer the country when the security forces could not even protect the seat of power.
But, looking relaxed, Mr Uribe spent his first day telling people they must overcome fear and get involved in the struggle.
Nobody could stand on the sidelines as the civil conflict increased in intensity, he said.
On Thursday, President Uribe also spoke by telephone to United Nations Secretary General Kofi Annan - who has helped the previous administration in its peace effort.
UN spokesman Fred Eckhard said Mr Annan had accepted Mr Uribe's request to continue to provide his "good offices" to pave the way for a resumption of talks.
However analysts point out that UN help in Colombia failed to save the last set of negotiations.