“I have a 4 year old son. My ex signed the birth certificate, but is not the father. I know who is dad is but not where. How can I make him take a paternity and make him pay child support as well as get my ex off the birth certificate.”
At this point there is a presumption of paternity. You and your ex cooperated to sign this fraudulent birth certificate. To compound this, your ex has now held the child out to be his own for 4 years. At this point, I believe you will need your ex’s cooperation to get his name off the birth certificate. If you are willing to admit your fraud, and present that to the Court with the support of your ex, you still need to find someone (i.e. biological father) before you can serve them with papers to take a paternity test.
Think of the impact to your son. Is it best for him to lose the only father he has ever known in favor of an absent sperm donor?