Kenneth Lerer, a prolific investor who helped found HuffPost, has stepped down as chairman of BuzzFeed, the viral-happy website that has lately experienced turbulence after a sharp rise in prominence.

Mr. Lerer’s departure, which was first reported by Axios on Tuesday, was confirmed by two people with knowledge of the matter who declined to speak publicly. His investment fund, Lerer Hippeau, has not altered its stake in BuzzFeed, one of the people said.

A BuzzFeed spokesman declined to comment.

The immediate implications of Mr. Lerer’s departure for BuzzFeed were unclear. Jonah Peretti, the site’s founder and chief executive, has been the site’s principal leader of late.

BuzzFeed has struggled in the past few years after a period of significant growth. The bumpy ride has coincided with a broader reckoning for digital media outlets confronting hurdles like the increasing dominance of Google and Facebook in the online advertising market. In January, BuzzFeed laid off 15 percent of its staff, including dozens of journalists at its money-losing but prestigious news division, whose employees are now locked in a standoff with management over their efforts to have a recently formed union recognized.