Not sure it completely answers the question of how common they were but here are a couple of posts that are relevant that you might find interesting.
As a follow-up question: Is the phrase "Dead of Alive" merely a trope we see in the movies?
Yes, there were "Wanted" posters, but they were not as common as we are made to think. For one thing, a poster, even a public place (such as a post office), will only be seen by people who happen to be passing by that way. It's not a very efficient way of disseminating information. Reward notices would also be placed in newspapers, would be sent via telegraph, and would be sent to relevant institutions (police, sheriffs, marshals, Pinkertons, etc.).
I won't go further now, since I've linked more below, but if you have more questions, let me know. :)