How to make hair get thicker?

I have thin hair, well the individual strands are thick or average i just dont have a ton of strands so it looks thin. It used to be average then I got extensions a year ago and they pulled a lot out when they got removed. Is there anything I could do to make it get thicker over time. I'm willing to be patient. So far I've been taking GNC ultra nourish hair vitamins with biotin in them for like a month. Is there anything else I can do? Like any topical products?