Now to the Scriptures. Some of these cases on their own may seem to prove little. But when the consistency of them becomes apparent, they speak volumes.
Acts 14:23 - Paul & Barnabas ordained elders in every church in Derbe, Lystra, Iconium, and Antioch. Nothing is notable that would indicate any of one the elders is different from the others.
Acts 15 (esp. 2,4,6,22,23) - With the church and the apostles, the elders deliberate the question "except ye be circumsized ye cannot be saved". No one elder seems to be distinguished from another. They are mentioned as a body or group. Paul & Barnabas take the lead in opening the session, declaring how God was working among the Gentiles. Certain Pharisees rejoin against their testimony. Peter rebutts, recalling how God sent him to Cornelius. Quietened by Peter's address, the body listens to Paul & Barnabas again. Then James takes the lead in closing the session, giving his "sentence" (KJV; judgment, NAS). This might be taken as authoritative, as in James making the decision. But should it be? The apostles, elders and the whole church did not acquiesce to James because of his authority, but gladly agreed because it seemed good to them.[This James is not James the brother of John (Acts 12:2), but apparently James the Lord's brother; seems to be called an apostle by Paul in Gal. 1:19]
Acts 20:17 - Paul called the elders of the church of Ephesus to meet him in Miletus. He addresses them equally, as a body, exhorting them to feed the flock over which the Holy Ghost made them overseers. He met with them all, taught them all, exhorted them all, warned them all, and prayed with them all. No one is drawn to the forefront for special charges or recognition.
Phil. 1:1 - The church at Philippi has plural elders. Paul & Timothy write to the saints at Philippi. Bishops are addressed, but none more than others.
1 Thess. 5:12,13 - The church at Thessalonica has plural elders. Those that labour among and are over are a "them" plural. "And we beseech you, brethren, to know them which labour among you, and are over you in the Lord, and admonish you; And to esteem them very highly in love for their work's sake." None are said to "be over" them more, or to be esteemed more.
I Timothy 5:17-20 - Those who "rule well" are plural in number. While this is general instruction to Timothy to teach others, the practical application appears to be plural elders in a singular church. Who is going to count them worthy of double honour? Who is going to not muzzle them? Who is going to hear accusations? Who is going to rebuke them? The local church.
Hebrews 13:7,17 - "Them which have the rule over you and watch for your souls" are described in a plural manner. One is not said to rule more or to watch more, or that one is to be obeyed more or remembered more.
James 5:14 - The sick are to call to themselves the elders of the church. Admittedly, the author is writing a general epistle, but in a real-life situation the singular sick person is instructed to call elders plural. The lack of a presbytery or plural eldership might not make that impossible, but would certainly mitigate against it being readily followed.
Rev. 2:1,8,12,18,3:1,7,14 - I mention this passage because of the common view that the "angel" of the church is the (singular) pastor. If this is true, it seems to be so in exception to all other cases noted. Several possibilities exist, including the fact that angel in its simplest meaning is simply the messenger from or to the church in each of these places. Or as Hanserd Knollys contends, angel could be used figuratively as a collective noun representing the elders of the church (especially since this is a book of signs & symbols). Nevertheless, it seems that the main burden is for those against plurality of elders to show why their interpretation is not consistent with the rest of the New Testament.
Other mentions of elders in the churches or passages that might have application, IMO: Acts 11:30; Acts 13:1; Eph. 4:11; I Tim. 3:1-13; I Tim 4:14; Titus 1:5ff., I Pet. 5:1ff., & III John 9.
Side note - the same idea appears to be true when the church at Jerusalem appoints deacons. Yes, two rose to a prominence of sorts because of their gifts and activity. BUT, the church appointed seven men equally over the work and did not assign one a title or status over and above the others.