I am having H1b petition approved but stamping was never done .Is the petition valid ?

I am having H1b petition from my previous employer approved(Expired in September 2016) but i never used it.

It was never stamped and i did not travel on that.

I left the company and then i travelled to US on H4 visa(dependent)

My query is can i use the h1b petition or do i have to file new h1 next year.

Can my petition be extented and resuable.?For how many years it will be extended?

What is the process for that.

A new employer can file a cap-exempt petition for you using the old petition as reference. The new petition will carry its own term of 1-3 years depending upon the documents submitted and evaluated by USCIS.

You can continue to file extensions/transfers until you have exhausted 6 years inside US on H-1.