You can contact any Dawson's Creek cast member through this postal address:

Dawson's Creek
c/o The WB Network
Attn: [PLACE CAST MEMBER'S NAME HERE]
4000 Warner Blvd
Burbank CA
91522 USA

If you could not follow the above address, then here is an example:
Dawson's Creek
c/o The WB Network
Attn: Katie Holmes
4000 Warner Blvd
Burbank CA
91522 USA