Update: SEGA provides a statement:
After an immense ten years the voice actor for the legendary Sonic the Hedgehog has announced that he has retired from the long-running franchise. Roger Craig Smith announced the news himself on Twitter to the surprise of fans. The Sonic series is celebrating its 30th anniversary this year, so it’s not the best time for a step down of the role of the main character. We will have to wait and see who replaces Roger Craig Smith as the voice of Sonic.
Thanks to sonicgalaxy27 for the news tip!