Urban Thesaurus finds slang words that are related to your search query.
Popular Slang Searches
The Urban Thesaurus was created by indexing millions of different slang terms which are defined on sites like Urban Dictionary. These indexes are then used to find usage correlations between slang terms. The official Urban Dictionary API is used to show the hover-definitions. Note that this thesaurus is not in any way affiliated with Urban Dictionary.
Due to the way the algorithm works, the thesaurus gives you mostly related slang words, rather than exact synonyms. The higher the terms are in the list, the more likely that they're relevant to the word or phrase that you searched for. The search algorithm handles phrases and strings of words quite well, so for example if you want words that are related to lol and rofl you can type in lol rofl and it should give you a pile of related slang terms. Or you might try boyfriend or girlfriend to get words that can mean either one of these (e.g. bae). Please also note that due to the nature of the internet (and especially UD), there will often be many terrible and offensive terms in the results.
There is still lots of work to be done to get this slang thesaurus to give consistently good results, but I think it's at the stage where it could be useful to people, which is why I released it.
Finally, you might like to check out the growing collection of curated slang words for different topics over at Slangpedia.