Hi Mohammed,
last year the vExpert nominations were announced at http://blogs.vmware.com/vmtn/. So watch this blog and you will know when the vExpert 2013 nominations start. Probably somewhere between today en the end of April. You can also search voor the #vexpert hashtag on Twitter. When the nominations start you will find a lot of tweets with this hashtag. You normally have one month to nominate. So it is no problem if you find out about the nominations a few days late.