Two branches of NI21 no longer exist – including one in the leader's own back yard.
Last night the remaining members of Lagan Valley NI21 – believed to be 10 – quit.
It represents a major blow for leader Basil McCrea, who represents Lagan Valley in the Assembly.
NI21 won its only council seat in Lisburn last month, and it was the new party's strongest area.
It is understood that councillor Johnny McCarthy was not on the executive of Lagan Valley and remains a member of the party.
Last week former council candidates Neil McNickle and David Honeyford resigned from the same constituency.
Meanwhile, the Queen's University Belfast branch of the party has dissolved itself and donated remaining funds to charity.
In a statement published online, the executive committee of the Queen's branch said: "The executive have been increasingly concerned about the nature of politics within NI21, but would like to emphasise the potential that the individuals and ideas of the party have with regard to changing Northern Ireland for the better.
"This was shown via the 11,495 votes gained by the party in the local council elections. The good people that were a part of NI21 should remain committed to engaging with our political institutions and strive for better."
The statement added: "The NI21 society recently held a fundraiser from which all money raised we intend to donate to local charities. This is not the end for a better Northern Ireland."
NI21 has been imploding since the May council and European elections.
The party descended into chaos after its executive proposed dropping its unionist designation at Stormont two days before voters went to the polls.
It then emerged that deputy leader John McCallister had initiated an inquiry against Mr McCrea into claims of inappropriate sexual activity involving female party workers.
But that probe was halted by the party, and its executive threatened Mr McCallister with disciplinary action.
He later said NI21 should be "put down".