If you've been playing the Sim in your current household and then move him/her out, you should be able to visit the new home. Did you place them in a specific house or did you kick them out to find their own? If you know the house, you should be able to click on the house to visit, just like any other. If you kicked them out, you need to watch when they leave and see where they end up living. If you don't have a strong enough relationship with the Sims moving out, their house won't show up in map view with a tag because that's only for ones who are at least friends of your Sim. If nothing else, call them to come visit, ask them to leave, and then follow them home to see where they live now.
I hope this is helpful.