I see no need to use each in this case:

sub find_in {
    my ($data_ref, $string) = @_;
    my $result = 'no result';

    my ($key) = grep /^$string$/i, keys %$data_ref;
    $result = $$data_ref{$key};
    return $result;
}
[download]

Update: condensed and with a modified data set:

sub find_in {
    my ($data_ref, $string) = @_;
    return $$data_ref{ (grep /^$string$/i, keys %$data_ref)[0] || '' }
+ || 'no result';
}
sub look_for_data {
    my %hash = ( A => 'axxx' , B => 'bxxx' , C => 'cxxx' , D => 'dxxx'
+);
    print "d: " . find_in(\%hash , 'd') . "\n";
    print "A: " . find_in(\%hash , 'A') . "\n";
    print "B: " . find_in(\%hash , 'B') . "\n";
    print "Z: " . find_in(\%hash , 'Z') . "\n";
}
look_for_data();
__END__
d: dxxx
A: axxx
B: bxxx
Z: no result
[download]

Update 2: Added ^ and $ anchors as per jhourcle advice.

Update 3: Same again.