Using new/overrides etc methods? im a bit in a worry

[PT Exorcist]

I am designing a plugin system by my own to meet my needs.
There is the "interface" for all plugins that is like this:

public abstract class IrcPluginBase {
	private IrcClient _parent;
	public IrcClient Parent { get { return _parent; } set { _parent = value; } }

	public void SetParent(IrcClient parent) { _parent = parent; }

	public virtual void RawCommandReceived(string command) {}

	public void SendRawCommand(string command) {
		_parent.SocketRef.Send(command);
	}

	public void SendText(string nick, string channel, string txt) {
	}
}

then here is a plugin's 'RawCommandReceived' function:

public void RawCommandReceived(string command) {
MessageBox.Show("hey");
}
}

My main class should then do this:

foreach (IrcPluginBase plugin in _plugins) {
plugin.RawCommandReceived(msg);
}

The problem is that this last line is calling the abstract class' 'RawCommandReceived' and not the plugin's overrided one

How should I go around this? I also tried removing the virtual/override keywords and put "new" but still the same problem