Regex grouping matches with C++ 11 regex library

I'm trying to use a regex for group matching. I want to extract two strings from one big string.

The input string looks something like this:

tХB:Username!Username@Username.tcc.domain.com Connected
tХB:Username!Username@Username.tcc.domain.com WEBMSG #Username :this is a message
tХB:Username!Username@Username.tcc.domain.com Status: visible

The Username can be anything. Same goes for the end part this is a message.

What I want to do is extract the Username that comes after the pound sign #. Not from any other place in the string, since that can vary aswell. I also want to get the message from the string that comes after the semicolon :.

I tried that with the following regex. But it never outputs any results.

regex rgx("WEBMSG #([a-zA-Z0-9]) :(.*?)");
smatch matches;

for(size_t i=0; i<matches.size(); ++i) {
    cout << "MATCH: " << matches[i] << endl;
}

I'm not getting any matches. What is wrong with my regex?