Internet radio pioneer Pandora Media Inc. is bringing back its co-founder Tim Westergren to run the company as it faces increasing competition from streaming music services such as Apple Music and Spotify. Westergren will replace Brian McAndrews as chief executive of the Oakland-based company. McAndrews was named CEO in 2013. Pandora’s shares fell $1.03, or 9%, to $9.90 in midday trading on Wall Street after Pandora announced the change in its leadership.