The other three girlfriends require you to contact them by using the in-game internet.
Carmen and Kiki each have a profile on and Alexandra on in the "Party girl seeks man for NSA fun and blog material"- topic.
Usually, restaurants have little effect on the progress of a date.
Therefore it's not recommended to take your girl out to eat on your first date, but, for instance, to a cabaret or comedy club.
Like in GTA San Andreas, two of the girlfriends are introduced during the storyline.