Search in own blog by tags

I am new to wordpress so I don’t know if this is common or something just not possible. When I use the search function on my blog and I type in a known tag for one of my posts nothing appears. It just says no post found. Is it possible to find specific posts by tags? Right now only my categories are working correctly. However if I click on a tag from the tag cloud it works correctly. Is is possible to add tags in the search engine and not only search by categories? That is the purpose of tags after all. Thank you.