This comes after the sacking of Dan Malesela just three games into the new season prompted supporters to protest outside the club's headquarters in Port Elizabeth.
Mpengesi has pledged his support to new coach Eric Tinkler and the rest of the team, and assures the club has a vision that it aims to see out.
The letter reads as follows:
'Dear Chippa United supporters,
The club has had a difficult start to the 2018/19 season, which has been exacerbated by the change in coaching staff.
The Chippa United family is one that is built on memories of both happy and trying times, and you have supported us through it all.
I am aware that our supporters will not always agree with decisions taken at management level, but I urge you to trust our vision.
Development in it's nature is inconsistent, but we are in the process of building a team that will make an impact and compete at the highest level.
I therefore urge our true supporters, those who attend all our matches come rain or shine and travel the length and breadth of South Africa to rally behind our boys, to remain calm in this storm.
I commit myself, together with management, to give coach Eric, his technical team and the players all the necessary support to take the team to new heights.