Chris Hughes, co-founder of Facebook, told CNBC on Monday that he has not heard from CEO Mark Zuckerberg since calling publicly for the breakup of the social media giant.

"I still consider him a friend," Hughes said in a "Squawk Box" interview. "I don't have any personal, negative feelings for Mark."

"The issue is that his power has grown too big because we're not regulating our markets the way that we must," Hughes argued.

In a New York Times op-ed in May, "It's Time to Break Up Facebook," Hughes wrote that Zuckerberg and he last met in the summer of 2017, just months before the Cambridge Analytica data misuse scandal broke. Hughes described spending time with Zuckerberg's wife and daughter, discussing politics, work and family life, and then parting ways.

"I haven't heard from him since" the Times op-ed was published, Hughes told CNBC. "I'm not sure I will."

Zuckerberg and Hughes were college roommates at Harvard University, where they started Facebook in 2004. Hughes left Facebook a few years later to work on Barack Obama's 2008 presidential campaign.

With his op-ed, Hughes joined a growing list of former Facebook executives publicly voicing their concerns about the company.

"The most problematic aspect of Facebook's power is Mark's unilateral control over speech," Hughes wrote in the Times. "There is no precedent for his ability to monitor, organize and even censor the conversations of two billion people."

Zuckerberg responded to the Hughes piece in an interview with French broadcaster France 2. "My main reaction is that what he's proposing we do isn't going to do anything to help."

On Monday, Hughes told CNBC he has raised issues to Zuckerberg in the past. "I had talked to him quite a bit about a whole set of issues here."