I made added a new custom object into my app in my sandbox and pushed it to production using change sets, the object has been successfully moved, but for some reason i cant find the tab.I can also see the custom tab definition, but the tab is missing.
Every profile has tab settings for each object, so if you didn't include Profiles in your change set, then they are most likely defaulted to "Tab Hidden". In this case, they won't be visible.
In the setup menu, navigate to the profile(s) you wish to enable the tab for and edit the object for the given tab in object settings. Set the tab settings to "Default On" or "Default Off" and it will become visible.