"Twitter is hard to evaluate. They have a lot of potential. It's a horribly mismanaged company—probably a lot of pot-smoking going on there. But it's such a solid franchise it may even work with all that," the co-founder of PayPal and early Facebook investor said in a "Squawk Box" interview.
But Thiel said he would not call for the ouster of Twitter CEO Dick Costolo. "I'm not sure they could do that much better. The CEO can't really change things that much in these companies. You'd have to fire everybody and start over."
Thiel, who does not own shares of Twitter, said the founders of the social media site set the tone for the company's culture and it's hard to change.
"One of the paradoxes is when you have a business model as good as Twitter—where you have 140 characters, no one can copy it, no one can compete—you can be screwing a lot of other stuff," he said.
"The management can be B+. Maybe some people come in at 10:30 and leave at 5 p.m.," he said. "It feels like it's vastly underperforming its potential."
Twitter did not have any immediate comment, but one early Twitter investor did—in a tweet, which Costolo responded to tongue-in-cheek.
—By CNBC's Matthew J. Belvedere