I really enjoyed all of Danziger's books but the one that stood out for me was Remember Me to Harold Square.
From Goodreads: This summer could be a disaster. Kendra's parents have invited Frank, a 15-year-old she's never met, to stay with them. And they've planned a goofy scavenger hunt for the kids, including Kendra's bratty younger brother. They have to race all around New York City and visit places like the Empire State Building and the United Nations to find answers. But once they get started, Kendra doesn't mind the scavenger hunt so much, mostly because Frank turns out to be just as interesting as all of the sights.
I was completely addicted to that book - it was a really good romance story made better by the fact that the two characters became really good friends too.
Other Paula Danziger books include The Pistachio Prescription, The Divorce Express, The Cat ate my Gymsuit and it's sequel There's a Bat in Bunk Five . They are all very quick reads but great fun! I believe they are aimed at younger teens and are probably very tame by today's standards but I remember really enjoying them.