You must create a task to make this.
Code:
#include <amxmodx>
#define PLUGIN "Continuous HUD Message"
#define VERSION "1.0"
#define AUTHOR "U"
public plugin_init() {
register_plugin(PLUGIN, VERSION, AUTHOR)
set_task(1.0,"message",_,_,_,"b")
}
public message(){
set_hudmessage(255, 255, 255, 0.6, 0.02, 0, 6.0, 4.0)
show_hudmessage(0,"Continuous HUD Message")
}