Ex has my son and won't tell me when he's coming back

We do not have a custody or consent order (unfortunately). For the past 3.5 years since the separation, he has spent every other weekend with his father and a couple of times here and there during the week. The status quo has been to bring him to daycare on Monday mornings after the weekend visit. Today he texted me to say that he still has our son, and when I asked him when he’d be back he said maybe tomorrow. I told him about an appointment he has tomorrow and have now asked him 7 times in emails/texts and a phone call when he’d be back. No reply.

What is my recourse here in absence of an agreement. I am planning to file for some sort of custody soon, but need to get my son back asap. Can I just go get him? What if he won’t come to the door? Do I call the police? I want to make sure I give him the proper opportunity to respond, and to show that he isn’t responsive before I do anything.

What would you recommend I do in this situation?

Yes, you can just go get him, but his father doesn’t have to give him to you willingly, and if you involve the police, without a custody order, there is nothing for you to enforce. You should file an action for custody, and I would speak with an attorney in your jurisdiction to determine the likelihood of a status quo order being granted. If it seems feasible, and you want the judge to return the child to you immediately, you should also file a motion to maintain the status quo.