Nà cì qiúzhù rú shíchén-dàhǎi, zàiyě méi xiāoxi le.
That plea for help sank like a stone in the sea, and there was never any news again.
Tips
history
From Wang Shifu's Yuan-dynasty play 《西厢记》 (Romance of the Western Chamber), Act IV: 他若是不来，似石沉大海 - 'If he doesn't come, it's like a stone sunk in the ocean.' A heroine's complaint about an unanswered letter - the modern usage is unchanged.
usage
Always about something sent out that gets no response - letters, applications, proposals, messages. Not used for physical objects that are lost; for that, use 杳无音信.
