Referal link problem

Question

hi
i want to creat referal links in my site . Like free lancer use reference links, every user have a referal link for exampl. [email protected]/yio1235.when user send this link to anyone and the reciever click on the link then sign up page of freelancer is opend and user signup there.
the confusion is that my site have signup page www.pics.edu.pk/signup.  but when a user have referral link you can say. www.pics.edu.pk/signup/456879.
and when someone click on this link page can not be opened because we dont have a page with link www.pics.edu.pk/signup/456879.
so how can i solve this?