Moeen Ali said he is "sad" to see Alastair Cook step down after 59 Tests as England Test captain.
The Worcestershire player has featured in every Test under Cook that he has been available for since making his debut three years ago.
The 29-year-old tweeted: "Sad to see Cooky step down! Legend of a person and always backed me. Thanks skip! "
David Leatherdale, PCA Chief Executive and former Worcestershire CCC CEO, said: "We are sorry to learn that Alastair Cook has decided to step down after captaining England in a record 59 Test Matches. We appreciate that this must have been a very difficult decision for Alastair to make.
"Alastair should be proud of his achievements as England captain having led the side to Ashes series victories in 2013 and 2015 plus away wins in India and South Africa during his four-and-a-half years in charge.
"Throughout his time as captain Alastair has been an outstanding ambassador for English cricket and the perfect role model for all professional cricketers.
"Alastair has also been a good friend to the PCA by kindly supporting our fund-raising events and generously helping the PCA Benevolent Fund during his Benefit Year in 2014. We are very grateful to Alastair for all his support.
"Alastair's decision to step down as captain is not, of course, the end of his Test career. I am sure that he will continue to score heavily and add to his phenomenal record as a batsman at that level."
Appointed in August 2012, Cook has led the team through more Test matches than any other England captain.
His record includes Ashes victories at home in 2013 and 2015 as well as series wins in India and South Africa.
He also led the one-day side for 69 one-day internationals between 2010 and 2014, another England record.
Cook discussed his decision with the Chairman of the England & Wales Cricket Board, Colin Graves, on Sunday evening and has confirmed his continuing commitment to playing Test cricket to Director of England Cricket, Andrew Strauss, and the selectors.
His resignation has been accepted, the Board have been informed and the proper process has started to appoint the next Test captain – the 80th in England’s Test match history.
The 32-year old opening batsman is England’s most capped Test captain, has scored more Test centuries than any previous captain and is England’s most prolific Test batsman with 11,057 runs in 140 Tests to date.
During his five seasons at the helm he was named Wisden Cricketer of the Year  and ICC World Test Captain  and his services to the game were recognised with a CBE – collected at Buckingham Palace last Friday, 3 February – to follow the MBE he was awarded in 2011.
Confirming his decision, Alastair Cook said: “It’s been a huge honour to be England captain and to lead the Test team over the past five years.
“Stepping down has been an incredibly hard decision but I know this is the correct decision for me and at the right time for the team.
“I’ve had time to reflect after the India series and this weekend I spoke to Colin Graves, the Chairman, to explain and offer my resignation.
“It’s a sad day personally in many ways but I want to thank everyone I’ve captained, all the coaches and support staff and, of course, the England supporters and the Barmy Army who follow us home and away and have given us unwavering support.
“Playing for England really is a privilege and I hope to carry on as a Test player, making a full contribution and helping the next England captain and the team however I can.”
Director of England Cricket, Andrew Strauss, today paid tribute to Alastair Cook and explained the next steps in appointing a successor, saying: “I want to thank Alastair, on behalf of the ECB and from a personal perspective, for the fantastic contribution that he’s made to the England Test team since taking over as Captain in 2012.
"His country owes him a great debt of gratitude; he's led the team with determination, conviction and a huge amount of pride over the last five years and his record stands for itself. With more matches leading the team than anyone, including two Ashes wins, he deserves to be seen as one of our country's great captains.
“Off the field as well as on, he has shown his strengths, developing the team and its culture, managing a fundamental transition and helping us to build for the future. As with all leaders, there have been times where circumstances have tested him but his resilience and temperament have helped him to prevail and to prosper.
“He has always served with the best interests of the team in the front of his mind and stays true to that as he steps down from the role. Alastair will be missed in his capacity as Captain but I hope that he has a number of years left to add to his record-breaking feats as an opening batsman and look forward to his continued success.
“We now move on with the process of appointing the right successor. There are a number of established players who are playing formal or informal leadership roles and whilst we've rightly not spoken to anyone in relation to the Test captaincy so far, we can now talk fully and openly within the team. We expect to be able to make an announcement before the team head to the West Indies on 22nd February.”
ECB Chairman Colin Graves said: “Alastair called me this weekend to offer his resignation and to explain the reasons behind it. This was clearly a very hard decision and I thoroughly respect the way it’s been made, with the team at the core of his thinking.
“His leadership has brought some huge successes for the England team and even in difficult times he has always shown his character, stayed composed and seen things through.
“Over the last two years he has also paved the way for our future and his work will help the transition to the next Test captain and the further development of this team. As he continues to play for England, I know that he’ll be very supportive of his successor and the next generation of players.
“Of course, as a batsman he’s one of the all-time greats. We owe him our gratitude, thank him for his commitment to England and look forward to watching him score plenty more runs for England.”
Tom Harrison, Chief Executive Officer of the ECB, also paid tribute and said: “Alastair has played a huge role as England Test captain and he is without any doubt a fantastic ambassador for the his country and for the game.
“His character, commitment and integrity stand out; he’s been an outstanding Captain for us, leading by example as he does at the top of the order. It’s no coincidence that he’s our most capped Test captain and our most prolific batsman ever.
“Through the ups and down that you experience with any long tenure he’s been courageous, consistent and resilient, handling everything with poise and dignity. I feel very fortunate to have work with him as Test captain, with Alastair giving us stability in the dressing room on and off the pitch.
“We owe him our sincere gratitude and I look forward to his continued success as part of the England Test team.”