Goodkind, who set up Frank alongside group MD Andrew Bloch in 2000, made the announcement in a LinkedIn post on Friday.
He wrote: "A lot of people have been asking and speculating, so I thought it worth updating and clarifying my current work status. I have, to use a bit of a bullshitty business term, 'gone plural'."
"I will be working across several companies and interests I have in addition to getting involved in exciting new projects... as part of that, I’m still very much active at Frank as its chairman, founder, and largest individual shareholder, although now 30 per cent of my working week is being spent in this role at the great agency I set up back in 2000."
Bloch told PRWeek: "Nothing has changed in regards to the day-to-day running of the business. The UK management team consisting of Andrew Bloch, Alex Grier (MD), Damon Kelly (group CFO) and Polly Atherton (director) continue to look after operations, clients and the running of the London, Manchester and Glasgow offices."
He also said Goodkind "provides counsel and advice and acts as a sounding board for the UK management team".
Frank has recently won work with Tyrrells, Photobox, the Israel Government Tourist Office and Volvo, for whom it has helped launch the new XC40 SUV model.
The agency was sold in 2007 to The Photon Group (now Enero), which now holds 75 per cent of the firm - Goodkind's stake is around 11 per cent, while MD Alex Grier and Bloch hold nearly seven per cent each.
Frank has featured in the upper half of the PRWeek UK Top 150 for several years, although staffcount and revenue dropped by more than 10 per cent to 44 employees and £5.3m respectively in the 2017 table.
Goodkind told PRWeek that none of his other projects or organisations were in the PR agency world. They include the charity Shift Foundation, business improvement district Camden Town Unlimited and Bird Restaurants, in which Bloch is also an investor, as well as a property portfolio.