Atiku urged politicians to put an end to the culture of political disunity that is tearing Nigeria apart.
The Mace, which is the symbol of authority of the Senate, was carted away by some hoodlums allegedly led by the suspended Senator Ovie Omo-Agege.
In a statement issued on Wednesday in Abuja and published on Facebook, Atiku said he is disappointed.
"I am utterly embarrassed, shocked and outraged by this ugly development because it is not only a threat to a major democratic institution but also represents a grave danger to the survival of our democracy," he said.
Atiku noted that using illegal and unconstitutional methods to threaten the authority of a key democratic institution is evil and unacceptable.
He wondered how the thugs could force their way into the Senate chamber and steal the Mace.
"If criminals could commit such security breach with impunity, it means that our entire democracy is in danger. Those behind this illegality to avoid creating a monster that could consume them.
"It is unacceptable and reprehensible to subject the National Assembly to this intimidation and humiliation. This attack by thugs should not go unpunished no matter who is involved", the former vice president added.
Atiku appealed to those heating up the polity to desist from it in the interest if Nigeria's hard-earned democracy.
Meanwhile, the police have arrested Omo-Agege and five other persons who allegedly stole the mace.