  This paper investigates when users create profiles in different social
networks, whether they are redundant expressions of the same persona, or they
are adapted to each platform. Using the personal webpages of 116,998 users on
About.me, we identify and extract matched user profiles on several major social
networks including Facebook, Twitter, LinkedIn, and Instagram. We find evidence
for distinct site-specific norms, such as differences in the language used in
the text of the profile self-description, and the kind of picture used as
profile image. By learning a model that robustly identifies the platform given
a user's profile image (0.657--0.829 AUC) or self-description (0.608--0.847
AUC), we confirm that users do adapt their behaviour to individual platforms in
an identifiable and learnable manner. However, different genders and age groups
adapt their behaviour differently from each other, and these differences are,
in general, consistent across different platforms. We show that differences in
social profile construction correspond to differences in how formal or informal
the platform is.
