- Shares traded at 10 times their normal trading volume Thursday.
- The stock hit an all-time high of $38.09.
- Dropbox went public in March, soaring 35 percent on its first day.
Dropbox saw its best day since going public Thursday, with massive trading volumes sending shares up roughly 20 percent at their peak.
The stock closed 14 percent up at $36.12, after hitting an all-time high of $38.09 earlier in the day. Shares traded at 10 times their normal trading volume.
Thursday's surge lifts Dropbox roughly 80 percent over its IPO price of $21.
Dropbox debuted on the public markets in March, soaring 35 percent on its first day. The company offers cloud storage for personal and enterprise use.
There's no obvious reason for the rally, but Dropbox has been pegged as an acquisition target in the past. In an April note Piper Jaffray analysts led by Alex Zukin flagged Apple, Salesforce, Cisco, Google and Microsoft as companies with the potential to buy Dropbox.
Before Thursday, the stock's largest single-day gain since its opening day topped out at 7 percent.
A company spokesperson declined to comment when contacted by CNBC.
--CNBC's Jordan Novet contributed to this report.