Ask HN: Cofounder signed off on Sales Agreement and has disapeared. What now?

I was involved in a prior start up over a year ago, which to make a long story short, I sold my interest in to the founder. Now, the founder (who relocated overseas) has become non-responsive and unreachable by any means of communication, and has yet to fulfill the obligation of the sales agreement.<p>1) Has anyone else been in a similar situation? 2) What are my options?<p>Any and all advice is welcomed, thank you for taking the time to read my post.