AMC’s stock plunges toward a record low after prospectus filed for sale of up to 40 million shares

Shares of AMC Entertainment Holdings Inc. plunged in active trading Wednesday toward a record low after the movie-theater operator disclosed an equity-distribution agreement in which the company could sell up to 40 million common shares.

The sales could represent up to 7.7% of the 519.2 million common shares outstanding as of Aug. 4.

AMC’s…