RadioShack ( RSH) financial chief Michael Newman is leaving the company to take a top post at a private equity firm with ties to the Blackstone Group. The company said Newman, 47, will take the financial chief job at Blackstone Crystal Holdings Capital Partners. His resignation takes effect Friday. RadioShack said David Johnson, 51, will take over as interim financial chief at the Fort Worth, Texas, electronics retailer. RadioShack said it is searching for a full-time chief financial officer. "We regret Mike's decision to leave RadioShack as he has been an extremely valuable asset to our management team," said CEO Leonard Roberts. "Mike helped build great bench strength within our finance organization and has helped us construct a sound financial platform -- one that positions us for long-term growth. In fact, as one of the architects of our longer-term growth strategy, Mike will be with us when we review the strategy at our upcoming board meeting next week. We thank him for his contributions to our company." On Wednesday, RadioShack slipped 36 cents to $28.17.