Members of Friends of Anna Scher include Martin Kemp, former Culture Secretary Chris Smith and Irvine Welsh.
Ms Scher herself is still in limbo, waiting to see if she will be allowed back to teach at the theatre she opened in 1968.
Last month its director, Andy Smith, also handed in his notice, claiming that the row between Ms Scher and the board of trustees made his position "untenable".
Ms Scher told the Standard: "I'm really quite bewildered by what's happened. It appears that the board of trustees want my name, my reputation and my theatre - but they don't want me."
The board of trustees will now seek advice from the Charity Commission about the theatre's future. Now Ms Scher has to await the outcome of the investigation.
"There's been too much bad feeling," she said. "All I want to do is teach and if I can do it in my theatre, that's great.