If your Tumblr blog is lost or stolen, there are a few things you can do to try and recover it. First, contact Tumblr and ask for help. They may be able to help you find the blog on their servers or help you get a new account set up. If that fails, you can try to find the blog on Google or other search engines.
If that fails, you can try to contact the blogger who created the blog and ask them to re-upload it to their website or blog. Finally, if all else fails, you can create a new blog and start over.