Krichefski will now manage a team of eight as well as advise BLM group clients on digital and search.
He will also be responsible for business development and strategy as well as growing BLM's search revenues. Krichefski will report to BLM Quantum's managing director Dan Clays.
His previous experience includes setting up the digital function at Initiative Media and St Lukes' digital offering, Klondike.
The latest purchase follows on from BLM's acquisition of premium and luxury goods specialist agency Red Media, in January.
Whereas many media agencies out-source search requirements, Krichefski will now fold his own company, KWord, into BLM. KWord has created search engine optimisation and pay-per-click campaigns for clients such as Travelocity, Best Foods, Citroen, Clarks, Lever Faberge, Saab, Sky and Unilever.
Last month, BLM Quantum picked up the £10m digital account for credit card business MBNA. Billings at the digital specialist have increased from £10m to £40m in the past two years, according to the agency.
Clays said: "Clients don't want to use several different digital agencies for their creative, planning, SEO and search marketing - they want it all in one place.
"Search is a critical part of the customer journey and Josh is a senior industry figure with a traditional media planning and strategy background coupled with unrivalled knowledge of the search business."
Clays added that he wanted Krichefski to work with the company's existing search marketing team, but also with the planners and affiliate marketing team.
"We are investing to make sure we are developing across all areas of search," he said.
BLM acquired Red Media in a multi-million pound deal. Since then the division, now called BLM Red, has been working with Quantum to establish how best to serve luxury clients through internet advertising.
Launched in 1994, Red's clients include clothing brands Diesel, Paul Smith, Gant and Aquascutum with annual billings of £10m.