I believe you can yes; even if you don't know them or see them, if they've impacted your life in someway you can miss a feeling they gave you (eg a TV character that can make you laugh) and when you get the feeling again it can make you think of that person.
Hope that makes sense but that's kind of my idea of why I think you can miss someone.
yes,it's possible to miss someone you've never met.I miss my fave movie characters and movie celebs who died(like Paul Walker) and even some animals that died or were killed(like Cecil,the lion from Africa)
Yes, I think so. Like celebrities, who are still alive or who have passed away. Or fictional characters from Tv shows who have been killed off or just left, or anyone I suppose. I mean, I miss a couple of celebrities, who have passed away like Heath Ledger, Cory Monteith, Brittany Murphy, etc. So, yeah, you can.
Yes. asides from fictional characters and actors you like, the internet provides a good source of that. Like how you can miss an online friend you haven't chatted with in a while, even if you've never met that person in real life.