You won't see the modem in your tracert, it's a bridge.
Are you certain that your modem has a web server built-in? If not, game over.
Most of the modems I'm familiar with that do have web servers have them at 192.168.100.1 (not changeable). Since most home networks are 192.x.x.x networks, it usually requires nothing more than changing netmask on your workstations to place that address on your network (255.255.255.0).