The Hastings Pier Charity, which employs 44 people, has gone into administration.
The pier, which first opened in 1872, fell into disrepair during the 1990s because of storm damage and neglect, and was finally closed to the public in 2008.
The structure was badly damaged by fire in 2010, but a group set up to save the pier persuaded the local council to allow it to take over the structure through a charity established in 2011.
In 2012, it secured a grant of £11.4m from the Heritage Lottery Fund towards the cost of restoring the pier, which reopened last year.
In a statement made on Friday, the charity said it had agreed a three-year business plan with the Heritage Lottery Fund, Hastings Borough Council and East Sussex County Council to reach self-funding status in three years.
But the plan required a further £800,000 and the charity thought it would be wrong to ask community shareholders for more money to fund the ongoing operating costs of Hastings pier, according to the statement. It said the major stakeholders did not feel able to support the new three-year plan.
"Sadly, therefore, the Hastings Pier Charity has been placed into administration," it said. "The board will do everything to assist the administrator and step down at the end of the year."
The charity said no staff would be made redundant and "the pier will remain open to the public whilst the administration takes place, and the pier will be fully operational and staffed for 2018".
In 2013, the organisation became the first charity to deregister and become a community benefit society with exempt charity status. Community benefit societies were set up for organisations that serve the interests of a community and are run by shareholding members.
Finbarr O’Connell and Adam Stephens of the consultancy Smith & Williamson have been appointed joint administrators of the charity.
O’Connell, joint administrator and restructuring and recovery partner, said he anticipated "extensive talks with local stakeholders" to find a "long-term sustainable solution". He added: "We are already talking to one party that is seriously interested in the pier."
Stephens, lead administrator and partner in the restructuring and recovery services department, said: "The trustees sought professional advice, and this suggested that administration would better position the charity to restructure itself and move forward to a successful outcome for this heritage asset.
"No employees have been made redundant in this administration and the administrators intend to work with staff, the previous trustees and local stakeholders to guarantee a sustainable future for it."
Amber Rudd, the Home Secretary and Conservative MP for Hastings and Rye, described the news as "very disappointing".
"Now we need a solution for all parties to work towards, which will provide the pier with a sustainable future," she said in a statement.
This year the pier won the Royal Institute of British Architects' Stirling Prize for being the best new building in the UK.