If this is the same alert system that was in Bitcoin and Litecoin (same meaning you just changed the key and not how it actually works), then it is vulnerable to several Denial of Service Attacks and you should remove it from your coin immediately. Please read
https://bitcoin.org/en/posts/alert-key-and-vulnerabilities-disclosure.
If you really want to send an alert anyways, you can download this file:
https://gist.github.com/laanwj/0e689cfa37b52bcbbb44 and read the comments. It has instructions on how to use it. Note that it may need some modification.