I've attempted to gather the biggest one-day-gainers all over the world. The list might not be 100% complete, but this is not information that's easy to parse.
Here's the list and the (sometimes stupid) reasons the stock popped.
1. Active Apparel Group popped 820% of December 28th 1998.
The stock went up over 800% after the company announced they planned to sell Everlast workout clothes online.
2. Enzo Biochem popped 400% on December 4th 1991.
The biotech company announced it has started to test a vaccine for treating HIV and Aids.
3. Moscow Cablecom popped 364% on February 1st in 2000.
Pretty close to the dot.com-peak the company announced they were offering fiber to their TV-customers. The market went nuts.
4. G-III Apparel Group jumped 317% on December 29th in 1998.
This was a one day 3-bagger without any news. The only news it needed can be found in the first entry on this list, Active Apparel Group.
5. China Natural Resources popped 316% on December 17th in 1999.
The company surfed in the wake of the trade agreement between US and China. This regardless of disappointing sales.
6. Media Services Group jumped 309% on April 12th 2004.
After announcing the purchase of a company with contracts with the US Army, Future Developments America, the investors went nuts.
7. SigmaTron International popped 244% on December 7th 2001.
Sometimes all you need is some bullish outlook.
8. Smith Micro Software jumped 232% on December 9th 1999.
This is the 8th biggest one-day-gain I have found in history, and it has no apparent explanation.
9. Abatix jumped 214% on April 15h 2004.
The rally was triggered by a deal with the company RapidCool.
10. Books-A-Million popped 200% on November 27th 1998..
The book company, I frankly have never heard of, said they were taking on Amazon.com.
Honorable mention:
A company that creates medical-marijuana dispensing machines itself said its stock was getting way too high this fall. The company Medbox popped about 3000% in one week in November. Marketwatch did a nice writeup on it.