They can work.

Usually don't.

The distance must be a transitional stage. 

There must be an active, achievable plan to eventually be together in person.

Nothing compares to seeing your significant other walk into the room, to being able to kiss their cheek and feel their warmth. 

I will, however, say that internet relationships can often result in a deeper mental/emotional bond than in-person relationships can. When all you truly have is words, every word becomes meaningful.

That's all.