You most likely have a bench warrant for your failure to appear. The court issues these to defendants who fail to show up to court. This means that you face arrest any time you interact with the police. The best course of action right now is to contact the court clerk directly and set your matter back on calendar. This will show that you were trying to clear it up should you be arrested. When it is placed on calendar, SHOW UP, and explain to the court why you missed. More likely than not, the court will recall the warrant. You may face a $300 - $400 civil assessment for missing court, but this is better than spending the night in jail. Good luck.
If you have a court date coming up this month, make sure to appear in court with proof that you no longer own the car (the DMV documents showing the sale). If you do not have a new court date, contact the court to get your matter put on calendar immediately.
First, there may be a bench warrant for your arrest. This depends on when you missed your court date, ect.
Second, you need to bring proof that your family no longer owns the car.