Move around. Sometimes a little, sometimes a lot. For at least a while there, most/all the gains came outside regular hours.
The vast majority of the news that move stocks (earnings reports, takeovers, mergers, new stock offerings, movements in foreign stock markets) occurs while the U.S. market is closed. The changes to stock price during the pre- and post- markets usually immediately reflect this news.
On the same subject traders can read the book "After Hours Trading Made Easy: Master the Risk and Reward of Extended-Hours Trading", by Joe Duarte.
Their movement would be dependent on factors like events having a ripple financial effect, particular company news, etc.