If you're the GM, it's your job to make sure things move forward.

Sadly, most RP goers are relatively poor communicators, and they won't speak up unless personally addressed. If they are waiting on someone to post, going on vacation, etc, chances are they are staying silent. It's also not uncommon for people to ghost or flake. Flakes in particular are a problem because they will constantly tell you that they are going to do something and never will. If you're the GM, you should let everyone know via OOC or discord that you are going to post soon and move everything forward. Sometimes people lose track of time, etc. Don't be angry or belligerent, but staying silent is not the answer.

As for 1x1 RPs, that's something I've had little luck with. But I don't see how speaking up can hurt.