we should show a public vote in 'no' confidence of Prime Minister Theresa May

Enough is enough, Theresa's deal is not good enough, she IS a remainer, and her deal is a remainers deal, and HER remainer MPs are trying to keep us in the EU, she is not doing what she was brought in to do, that is deliver what the majority of the electorate voted for. we need her gone

We can't accept petitions about appointments, which includes calling for Ministers, including the Prime Minister, to be sacked or for a vote of no confidence.

If you're concerned about a particular policy or decision that's the responsibility of Government or the House of Commons, you could start a petition about that.
Petitions calling for action on policy are more likely to be an effective way of achieving the change you want.