Facebook has reported a slowdown in sales growth, which has failed to quell fears about its ability to boost advertising.
Revenue rose 32% to $1.2 million in the three months to June, its slowest pace on record, while margins decreased.
The Mark Zuckerberg-founded company did not provide any earnings forecasts, prompting a sharp fall in its share price to record lows of under $US24 a share.
Shares had debuted at $US38 each.
Investors want reassurance that Facebook can compete against Twitter and Google, and that it can overcome challenges making money from advertising on mobile devices.
The company says the number of monthly active users is up to 955 million.