My girlfriend has left with our 3 month old baby girl and I don't know what exactly where they are, what can I do?

I would suggest considering filing a petition to establish decision-making (custody), parenting time (visitation) and child support. You will need to outline the last known whereabouts of your daughter. You can also file for temporary orders requesting that the child be returned to you. Then the issue will be serving the mother with the paperwork. Often clients can track down the mother through facebook contacts and other information. We do have the ability of hiring private detectives or running a skiptrace to see if she has surfaced.

If I were you, and I had the means, and I had already determined after 1) asking around discretely among my friends and family where the mother and child may be; and 2) doing a search of Google, Facebook, and any other social media sites that my ex-girlfriend uses or may have used in an effort to find her, I would hire a private investigator to track her and the child down. Then I would use that information to continue to track mother and child while I file a petition to adjudicate paternity, and to have an award made by the court regarding child custody.

File a petition for custody and child support and have the process server find her and serve her.