Can anybody please check my English?

[kekekekek]

*That* is simply because online advertisements can *reach* the broadest *audience.* In-person promotions (I think that's what you're trying to say?) are only available for people who pass by the person who is distributing the flyers or the store *where* the poster is *displayed.*

But the amount of people that the online advertisements can reach is unlimited. Not only that we can put the advertising on widely used websites such as Facebook so it is automatically shown to *a lot of* (tons of people is colloquial you wouldn't use it in an essay) people, but *it will also* independently spread even *further* once it is put online.

For instance if *someone* finds a product that *this person’s* (or *their*) friend might also like, he or she can copy the link and share it with the friend instantly. (if at all possible, don't start a sentence with 'and') *The* friend *might* also share the link *with* ('to' is possible if you think about facebook, but 'with' sounds better in an essay) other friends. *From there* it can keep going since it is so easy to share the information of the product.

In addition, when people want to learn more about the product like the specifications, price, and stores that carry it, all *that* (there REALLY is not plural xD) information *is* available online so he or she can check *it anywhere,* anytime.

I also think online advertisements can be very cost effective. If you want, you can literally start *advertising* for free. All you have to do is *post* the advertisement on major social networking services and *it can be* shared widely if it is interesting in some way.

Although handing out flyers and displaying a poster in a store window are still good advertising methods, they cannot beat the convenience and *unlimited possibilites* of the online advertisement that *is* mentioned above.

That is why I believe online advertisement is the most effective way to advertise a new product as compared *with flyers* and posters.

keep in mind that not all corrections were actual 'mistakes' - mostly it just helps the flow of the text.