There are several virtual tabletops that will do what you need. My personal favourite is Roll20, you can upload your own maps and tokens, the free account comes with plenty of storage and features, and there's tons of additional features for keeping track of stats, dynamic lighting, rules integration, integrated voice chat, an extensive marketplace for tokens and maps, etc. I would recommend it. If you want something simple, I've heard good things about Owlbear Rodeo, but I have not tried it.