How to aproach when thesis supervisor just "disappear"?
I had one of those issues when I was doing a PH.D.  You should contact your supervisor first and cc the department head. That way you have more people in the loop. In that email, make an appointment.  If the supervisor doesn't get back to you, that's a red flag. You will be able to then speak to the department head about it and he/she will have some context when you see him/her. In that meeting with the head, speak about your issue. They will solve the problem. 

If your supervisor does get back to you, which I assume he/she will since the department head is now in the loop, don't be confrontational. Just have a normal discussion about how you couldn't get a response and that you need more help. 

That's how I'd approach it.