there's a lot of people on tumblr, and so if you just use one tag-especially one with a lot of people on it, like "fairy" it will probably not show up in search, because it will be buried so quickly by everyone else posting. So, I would use a lot more tags. And to try out different tags to see what might work better. Some people use an "artist of tumblr" tag other's use fanart tags, (I drew for a fandom that didn't have a lot of art once and it did pretty well) Concept art and character design is another tag that might find people?
Overall it doesn't matter too much if you come up in the top of search or not on tumblr--it's about whether people reblog you. You get way more action from reblogs than anything else, so just keep making new stuff, and keep experimenting with tags, and eventually you'll make something that will get reblogged. And, if it's a popular site, then that reblog will spawn more reblogs and etc.