click on Real Property Data Search, Select Baltimore City and select street address, then put in street address and click "search". The at give you the names of the owners and where they receive the tax bill and assessments.
I would recommend using public (and free) resources first. For example, the public record information. I've successfully used social networking websites like Facebook.com, Linkdin.com, and even Google.com searches to successfully contact hard-to-find homeowners. Another option would be to contact the last listing agent for more information. I would be happy to try to answer any questions you may have or you get information that would be helpful to you too. Good luck!