You need to quote the backslash. I've used \Q below. \Q (quotemeta) is described in Regular Expressions.

$_ = '\x2f\x2f\x2f' . "\n";
print;
print "Matched\n" if s/\Q\x2f/\//igs;
print;
__END__
\x2f\x2f\x2f
Matched
///
[download]

update: added link to \Q