chase after vs have a thing

chase after

verb
  • To pursue someone with romantic intentions; to woo. 

  • Used other than figuratively or idiomatically: see chase, after. 

have a thing

verb
  • To be in a casual romantic relationship. 

  • To have a crush on, or a soft spot for, someone. 

How often have the words chase after and have a thing occurred in a corpus of books? (source: Google Ngram Viewer )