A majority (59.48%) of Tory members now believe Mrs May should resign, according to a snap survey by the Conservative Home website yesterday.
It found that just 36.66% of the 1,503 respondents believe she should stay on.
The survey had not been carried out as a weighted sample as people self-selected to vote in it.
Editor Paul Goodman said the results were "astonishing" and "the most damning finding that in one of our polls that I can remember".
Labour have held their seat in Dudley North. The results had to be recounted three times. Labour MP Ian Austin retained his seat by 22 votes.
Theresa May will remain as Prime Minister and the Conservatives will be supported by the DUP in parliament.
Speaking after meeting the Queen at Buckingham Palace, she said she intends to form a government that will provide "certainty" and guide the country through Brexit talks.
She said she was confident that the Tories would be able to work together with the Democratic Unionist Party in the "interests of the whole UK".
Mrs May added that she will work for a "Brexit deal that works for everyone in this country".
Theresa May has said she intends to form a government that will provide "certainty" and guide the country through Brexit talks.
Mrs May said she was confident the Tories would be able to work together with the Democratic Unionist Party in the "interests of the whole UK".
Speaking outside Number 10, she said: "This Government will guide the country through the crucial Brexit talks that begin in just 10 days and deliver on the will of the British people by taking the United Kingdom out of the European Union.
"It will work to keep our nation safe and secure by delivering the change that I set out following the appalling attacks in Manchester and London.
"We will fulfil the promise of Brexit together and, over the next five years, build a country in which no-one and no community is left behind.
"What the country needs more than ever is certainty...now let's get to work."
Veteran David Winnick failed to defend Walsall North where his majority was less than 2,000. He had held his seat there since 1979.
Keith Wilkinson reports from Walsall:
Paul Nuttall has resigned as Ukip leader after his party failed to gain a single seat in Westminster.
The Ukip leader only managed to gain third place in Boston and Skegness as he failed to take the constituency which had the highest Leave vote in the EU Referendum.
He said: "I'm standing down today as the leader of UKIP with immediate effect. This will allow the party to have a new leader in place by the conference in September."
Andy Street, the Conservatives' West Midlands metro mayor, who beat Labour in the mayoral election last month, said Theresa May should stay on as Prime Minister but needed to start "listening".
Mr Street, former managing director of John Lewis, contrasted the "hope, optimism and inclusivity" of his own successful campaign run with the tone of the Conservatives' General Election pitch.
Speaking on BBC Radio 5 Live, he added that the Tories had failed to hammer home the message on economic stability and that "the risk around that changing, wasn't made clear around the last few weeks".
While backing Mrs May to stay on in the top job, he added: "The mark of the real leader is listening to what is being said over the last 24 hours."
Paul Nuttall has resigned as UKIP leader after he was defeated in Boston and Skegness.
He came third place in the count, his sixth unsuccessful attempt to get a Westminster seat.
There has been a very eventful night across the Midlands, with a number of momentous moments including the first female Sikh MP.Read the full story ›
Broxtowe MP Anna Soubry has said Prime Minister Theresa May should consider her position after 'a disastrous night for her party.'
She has been speaking to our reporter Peter Bearne: