It's hard to know what you're trying to achieve here. If grandma is taking care of the baby, because neither you nor mom want to shoulder that responsibility, then it can hardly be said that mom's abandoning the child - from what you have said, it appears to b your mutual choice to let grandma take care of the child.
If your concern is that your wife floats in and out of the house, doing as she pleases, treating you more like a hotelier or a babysitter than as a spouse... well, she's sixteen, and I doubt that anybody who's dealt with teenagers is going to be surprised by that. Neither maternity nor marriage will transform a teenager into an adult. You may have been happy during the time you thought you were being a perfect husband, but it seems more than safe to infer that she was not.
If she's not missing, there's no point in "reporting her missing". If the marriage isn't working out, there's always the option of divorce.

