ANSWER: The King James Version of the New Testament uses the phrase "church of God" eight times. Interestingly, it is only the apostle Paul, and not any of the other Biblical writers, who uses this term either in speaking or in writing. He uses the phrase involving the word church only twice in direct reference to a group of true Christians meeting in a particular city (1Corinthians 1:2, 2Corinthians 1:1).
Paul also states, in 1Corinthians 15:9 and Galatians 1:13, that before his conversion, he went after those in the church (a general reference to those who, primarily in Jerusalem, believed in Jesus).
The places where the words 'church of God' (or very close to it) occur in the New Testament do not refer to the official name of a religious organization or denomination (Acts 20:28, 1Corinthians 10:32, 11:22, 1Timothy 3:5, 15 and those mentioned above). They also do not refer to a building where those who worship God meet. These references are to those who are converted believers.
The Bible does not state that one can determine who is part of the "true church," meaning those who teach the same foundational truths as the early disciples, simply by the name of a fellowship group, organization, or denomination. In fact, attempts to label those who worship under the banner of a particular denomination or group as the entirety of true Christians on earth cannot be supported in Scripture and is foolishly self-delusional.
At any time, the group of all those alive who are converted and living the life of a true Christian are known only to our Father in heaven. The membership list of this unique group, personally called by the Eternal, is referred to as the book of life.
The Apostle Paul refers to this mysterious book in his letter to the Philippians when he asks the fellowship in Philippi to assist women who have helped him preach the gospel. These faithful believers, he states, had their names written in this special spiritual book (Philippians 4:1 - 3). Those who are not converted and therefore not "true church" members are said to not have their names written in this book known only to God (Revelation 17:8, see also 20:12, 21:27).
Delineating what beliefs might constitute a "true" group who teaches the same things as the early New Testament church of God is beyond the scope of this short answer.
That said, you can hardly go wrong by fellowshipping with those who worship God with 'fear and trembling' (Philippians 2:12), who love each other (John 13:35), and are of a 'humble and contrite spirit' (Isaiah 66:2). They should also behave like the Bereans, who 'examined the Scriptures daily to see if these things were so' (Acts 17:11).
God has always had only one true church. It is composed of all those, throughout history, who willingly obeyed him, through the power of the Holy Spirit, until their death.