First, see if you can locate her on social media, then check your state to see if they have a Birth Father Registry or known also as a Putative Father Registry that you can sign up with.
Birth father registries were established in a little more than 2 dozen states to help protect the rights of birth fathers’ in situations where they might have lost connection with the birth mother or she is ignoring you. These registries allow biological fathers to voluntarily acknowledge paternity, even if you only think you might be the father, when any child born outside of marriage. After you register with a state’s Punitive Father’s Registry, you will receive notice of any court proceedings regarding the baby, adoption petitions pending for adoption, and actions to terminate your parental rights. When the birth father is notified about an adoption through the Putative Father Registry, he can then decide whether he would like to do voluntary termination of his parental rights and be part of the adoption plan. This will help the legal aspect of the adoption to go smoother and you won’t been seen as the guy that caused more problems. It’s better to be seen as helpful and willing, to man up and be part of the solution then part of the problem. The Putative Father Registry is the best way for a guy to protect his parental rights.
If your state doesn’t have a registry, then keep trying to reach her. Contact mutual friends and family members. This child is yours too and discussing the options with her would be beneficial for you both.