If you're logged into the Lodestone yourself and search for a character by just using the little search field, the lodestone will only search for characters on your own world - if said tank was from a different world, they wont show up. You'll have to adjust the filters to search on all worlds (or a different, specific one if you happen to remember what world that tank was from).

You can set your lodestone-profile to "more private", aka displaying less information about your character on it for everyone to see, but your character will always show up.