Ian Mason has announced he will step down as chief executive of Electrocomponents at the end of the financial year, sending shares in the company shooting lower on Thursday morning.Mason, who has been chief of the FTSE 250 group for the past 13 years, said his decision followed the successful implementation of the group's 2012 strategy to increase market share and sales growth rates.The group has begun the search process for his replacement.Ian Mason said: "It has been a privilege to lead Electrocomponents for the last 13 years. The business has been transformed into a truly international group, with a strong and experienced management team and a clear strategy."With the group's five-year strategy successfully underway it is the right time for me to pass the baton. I will continue to serve the company until the end of March to help ensure a smooth succession."Shares had dropped 4.39% to 224.40p by 09:08.