activist interventions. Shares of Alphabet have fallen by roughly one-third this year, more than the tech-heavy Nasdaq Composite Index.

Meta came under pressure last month from the investment firm Altimeter Capital, which wrote in an open letter that CEO Mark Zuckerberg needed to take drastic steps to streamline the company.

Last month activist fund Starboard Value LP said it had taken positions in software-makers Salesforce Inc. and Splunk Inc.

Mr. Hohn said Alphabet should make the suggested changes as soon as possible, pointing to recent decisions by other big technology companies.

“If you look at Meta and Amazon, it hasn’t taken them long to get to grips with it and make their analysis and announcements,” Mr. Hohn said. “We don’t think it should take long at all.”

TCI held conversations with former Google executives who suggested the company could be operated more effectively with significantly fewer employees, it said in the letter. Alphabet’s head count has more than doubled since 2017, it wrote.

“You have publicly stated that Google should be 20% more efficient. We could not agree more,” TCI said in the letter.

TCI’s Mr. Hohn is a prominent investor who has made a name taking on some of the world’s biggest companies, usually in service of higher returns for shareholders but also for social causes. Last year he launched a campaign to force dozens of the world’s largest companies, including Alphabet, to publish carbon-emission reduction plans and put them up for shareholder vote.