Learn English – Single word for someone who likes to party

In addition to Edwin Ashworth's excellent suggestions of socialite and party animal I can make a few suggestions.

All of these uses are slang/idiomatic hence they might be readily available in a thesaurus or standard reference.

Partier (alternatively partyer) - usually a negative connotation.

He flunked out of college because he was too busy being a partier to study.

(Note - the proper usage of this term is to describe a party attendee. This usage is slangy.)

Clubber - similar to partier.

That girl is a real clubber! I always see her stumbling home at dawn!

(Note - the proper usage of this term is to describe someone wielding a club, typically to beat something like a baby seal to death.)

Also, an old-fashioned term: Good Time Charlie

I think this usage is quite antiquated, but it remains useful.