i rented a ground flr shop to tenant A few years back for restaurant

then half way, tenant A sold the biz to tenant B, which continue the tenancy but there is no formal new tenancy agt between me and tenant B

Few mths now Tenant B defaulted the rental and the shop is closed. Tenant B is having a tough time to sell his biz to another one, thats why he did not hand over vacant possession to me.

so if i want to get lawyer to send letter of demand, its to Tenant A or Tenant B ?

I personally think of course its Tenant B but some says there is no formal contract.

but if no formal contract, then i can just remove Tenant B's stuff from my shop ??

If no formal contract and tenant b refuse to move his stuffs, you can report to police then proceed remove his stuff.

Don't just remove his stuffs away.

Engage a lawyer to remove him legally. Send him few notices and get the police to help with the eviction if possible.

You don't want Tenant B to be a dick and get you in trouble.