made the title clearer 
Can anybody tell me what does it mean if you dream your son has disappeared?
We would have a better chance of being able to give an interpretation if we knew a bit more about the dream.
eg
How old was your son in the dream? have you a son in waking life? Was the dream son the same age?
How did he disappear?
BTW welcome to the forum 
I think its just a dream. I have random dreams like that all the time.
The best way to interpret it would be to use your own judgement…nobody but you can truly interpret a dream. Think of your fears, do you fear losing a son? Or possibly your son represents something else in the dream? It is a hard thing to ask someone else. Only you know the real meaning, unless you believe it is a premonition, in which case lock him in the basement! (Joke)