I think they can work... but most of them don't.
People like to lie about who they are, what they've accomplished, etc. It's too easy on the internet. People who engage in online relationships tend to be incredibly immature and more prone to fantasy (both creating it and believing it). I can count the relationships I've seen work based on online meetings on one hand... and all of them have been between experienced adults who were more or less honest about themselves.
I'm pretty sure I can write a book about the people I've known who had online relationships tank, have played pranks on others by pretending to be entirely different people, rp their lives away as fictional characters in fictional romances or have been the victim of an online boyfriend or girlfriend lying about their location/abilities/gender/job/etc.
Online relationships are a bad idea.
Meet the real thing before you commit to anything remotely romantic. And do your homework. Don't believe everything you hear just because you want to.