Milner, chief executive of Russia's Digital Sky Technologies, has defined a new style of investment in Internet companies in the last two years by buying stakes at a late stage and adding to them with employee and preferred shares.
DST bought a 2 percent stake in Facebook for $200 million in 2009, widely considered at the time to be an overpayment. Facebook's most recent fundraising round valued the social network at roughly $50 billion.
"I think you should at least wait until they go public," Milner said when asked at the Abu Dhabi Media summit about his exit strategy. His investment group has not yet exited any of the companies in which it has bought stakes.
"When the founder starts selling, you should start selling aswell," he added.
(Reporting by Georgina Prodhan)