Do you need published papers to apply for a postdoc? A friend of mine has a conundrum: He finished his PhD and wants to stay in academia (in Physics). Problem is, his supervisor is very unsupportive in everything. I think he switched research interests and left my friend hanging. He's extremely slow in working on a draft they want to submit to a high-tier journal, and my friend believes that without this work published it doesn't make sense to even start applying for postdocs.

Problem is that this has been going on for years now and thus his career has stagnated.

I feel that this can't be quite right, but since I never bothered to look into postdocs I might be wrong.

In my opinion, my friend should just apply for postdocs anyway, with or without all of the PhD work published. I have a hard time imagining that a successful application lives and dies with one particular paper. That would mean that anyone whose supervisor stops working for one reason or another would be forever stranded in limbo.

Tips and advice on how my friend could move forward would be appreciated.
All you need to apply for a post-doc is a the ability to write an application - getting an offer is another matter.  Most post-docs will have their PhD and will have published (or at least submitted) one or more papers in the course of that program.  If your friend has not yet published or submitted any papers then he will indeed be at a disadvantage in an application for this kind of position.  Having said that, you've got to be in it to win it!  If he does not mind taking the time to write up an application, it can't hurt to apply.  In the meantime he should keep working on his paper and pushing for further progress with his co-author.  If he can succeed in publishing this paper in a high-tier journal then that will substantially improve his applications.