To start, was this a good tenant that is now exhibiting out of character behavior or is this a habitual late/non payer? That is a huge difference on how to handle in my opinion. If this is a good tenant that just isn't responding and not paying then maybe something is wrong. Maybe do an occupancy check to make sure the tenant is still there (and alive. Sorry if thats gruesome). You could also check with an emergency contact if it's completely out of character. Last year I had a tenant who always paid on time and was super friendly not pay and not respond and turns out they had a stroke and were in the hospital. I would have felt horrible if I had filed eviction on her.
If this is a habitual late payer or bad tenant, or if your search above doesn't turn up anything, then I default to this...
What does your lease say? In PA the landlord tenant law states that unless you have it in writing, like a lease that states otherwise, you need to give 10 day notice to quit prior to filing eviction. Our lease waives that 10 day notice to quit so I would immediately file eviction. The tenant will either show up and then you can at least get some communication as to what is happening or they wont show up and you can file possession.
Hope everything turns out ok!