Kitson has agreed to terminate his contract, leaving midfielder Lawrence and defender Ben Haim as the only professionals left on the books as the club seek to avoid liquidation.
Administrator Trevor Birch warned on July 24 that the League One club would go out of business on August 10 unless an agreement could be reached over the wages of their senior players.
Three were left after Kanu effectively walked away at the end of last month, and the south-coast outfit announced on Friday that Kitson was also on his way out.
A club statement read: "Pompey have reached an agreement with Dave Kitson over the termination of his contract.
"The 32-year-old striker has signed a compromise agreement over money outstanding for the final year of his contract."
Birch said: "I'd like to thank Dave and his agent for the stance they've taken to give Portsmouth Football Club the best possible chance of survival.
"We thank Dave for his service to the club and wish him every success for the future."
Kitson scored 12 goals in 72 appearances for Pompey after arriving from Stoke in August 2010.