You didn't show any example of what was "not working", but this does.

my $string = "Happy Joy 002245:Dubloons 002256:hats 034523:paper clips
+ 232344:pants 233394";
my @items = split /:/, $string;
my $number;
$number = $1 if $items[0] =~ m/(\d+)/;
print $number, "\n";
[download]

Make sure not to use $number if a match didn't occur. Also, this method provides you with every item. I know you mentioned only wanting the first. If that's all you'll ever need, you can just do this:

$number = $1 if $string =~ m/(\d+):/;
print $number, "\n";
[download]

Cheers!