Deputy party leader Goran Kaurić said the anniversary was being marked in the village of Mala Bosna, outside the party's headquarters in Subotica for a second consecutive year.
He said party bodies had not met for more than a year and called for the swift election of a legitimate leadership.
"We must continue fighting for the political legacy of all Croats in this region, and we will not allow one man to systematically destroy our party," Kaurić said.
He described the situation as the party's deepest political crisis since its founding, warning that continued inactivity could erode voter support.
Kaurić also said the current leadership lacked the legitimacy to decide on DSHV's participation in elections for the Croatian National Council because internal party elections had not been held.
Former DSHV president Bela Tonković announced the establishment of a founders' club aimed at bringing together founding and long-standing members to advise the party after new leadership is elected.
In a statement published on DSHV's official website, which reflects Žigmanov's position, the party said it had faced "unprecedented challenges" over the past two years, blaming the crisis on "putschists" it says are coordinated by power centres outside the party.
Žigmanov has rejected accusations that he leads the party in an undemocratic and non-transparent manner, accusing them instead of illegally obstructing its work.
DSHV, founded in Subotica on 15 July 1990, is the largest and oldest political party representing Croatia's minority in Serbia. Žigmanov is its third president.