Typically, if we think of missionaries as those who cross cultural, linguistic, and political boundaries to preach the Gospel and plant churches, we go immediately to Paul and his band of missionaries. Not all of Paul's colleagues were "full time missionaries" in the sense that we think of today. However, there were over 20 individuals who specifically helped or collaborated with Paul in his missionary work. 3 John 5-8 indicates that, by the end of the first century, there were individuals and small teams of people supported by local churches that did missionary ministry across the Roman Empire. Old Testament prophets were sometimes impelled by God to take a message of God's greatness and judgment to other nations, most notably Jonah.

Reading the book of Acts and the rest of the New Testament, we see that missionaries in the Bible are the "sent ones" that includes the 12 apostles/disciples of Jesus, Paul, and his missionary team (s), and others who were sent out and went out preaching and evangelizing. See especially Acts 13:1-4. When we think of this question, naturally the issue of the cessation of the apostolic office comes up vs. the sense in which the gifting of "apostle", in the sense of missionary, is still valid today.

Pastor Sam Waldron has a very helpful section in his book on the Canon of Scripture, where he distinquishes between

  1. the apostles of Jesus Christ - the 12 and Paul, James, Jude. and
  2. the "apostles of the churches" - those others sent out by the churches that are not "Big A" apostles who had authority to write Scripture, etc.

That is a helpful distinction. Below is an extended section from Sam Waldron's book, which is online on the Canon of Scripture:

C. The Other Apostolates

1. The word, apostle, was used to refer to some who were apostles in the same sense as Paul and the Twelve.

BAG, the Greek Lexicon, asserts that apostle may refer to a delegate, envoy, messenger, or, perhaps, a missionary. According to its root words, the word simply means, "a sent one." Obviously, such a word could have a broad range of applications. It seems quite possible that it could be used of those who were not apostles in the narrow, official, technical sense in which the twelve and Paul were. Cf. by way of illustration the broader and narrower meanings elder, overseer, and deacon. All have other meanings or applications than to the office which they specifically designate in the church. The biblical usage of apostle shows that it was not restricted to what we may call "Big A-apostles".

a. Sometimes the term is used to designate the apostles of the churches. That is, the official messengers, delegates, or envoys of certain, local churches (Phil. 2:25; 2 Cor. 8:23). This usage may explain some or all of the other uses of the term when it does not refer to "Big A-apostles." We might say that these apostles were apostles of the churches not apostles of Christ. That is, they were sent with the authority of the churches and not with the authority of Christ Himself.

b. Sometimes the term is used of missionaries. That is to say, those sent out from churches to be gospel pioneers in other places. Notice Acts 13:3; 14:26; 15:40, though only the idea and not the term is present in these passages. It is probably in this sense that men like the following are called apostles. Barnabas is called an apostle (Acts 14:4), but he is not a "Big A-apostle" (Acts 4:36f). Timothy is termed an apostle (1 Thess. 1:1; 2:6), but he is not a "Big A-apostle" (Acts 16:1f.). Silas also is called an apostle (1 Thess. 1:1; 2:6), but it is not likely that he was a "Big A-apostle," (Acts 15:32). Apollos may be called an apostle (1 Cor. 4:9; 3:22; 4:17), but he is certainly not an
apostle in the strict sense (Acts 18:24f.). If Andronicus and Junias are designated apostles in Rom.16:17 (This is uncertain.), it would be in this lower sense. It is possible that such men were termed apostles because of their association with Paul in his apostolate to the Gentiles. This association gave to them, so to speak, a share in his ministry and authority. Notice especially 1 Thess. 1:1, 2:6. Certainly, Timothy and Titus were apostolic representatives. Thus, they were in possession of extraordinary authority (Titus 1:5, I Tim. 1:3;

2. It is also possible that this term is used to designate others who were apostles in the sense of the Twelve and Paul "Big A-apostles.
The references to James, the Lord's brother, may assign a "Big A-apostolate" to him. Notice Gal. 1:19; 2:9; 1 Cor. 9:5; Acts 12:17; 15:6-13; 1 Cor. 15:7. (I am assuming that all these references are to the half-brother of our Lord. I believe this to be the most likely interpretation of these passages.) One may easily interpret such verses as ascribing to James an apostolate parallel to that of Paul. He had seen the resurrected Lord--perhaps like Paul he had been converted by the sight. Perhaps at that time he was appointed to a special apostolate to the Jews like that of Paul to the Gentiles. The reference in 1 Cor. 9:5 to "the brothers of the Lord" may mean that a similar apostolate was given to Joseph, Simon and Judas. Notice Matt. 12:46f; John 7:5; Mark 13:21; Matt. 12:46f; 13:55, and Acts 1:14.

D. Conclusions

1. This survey of the usage of the term enables us to make a distinction between a broader and narrower usage of the term in the New Testament. This distinction is clearly demanded by the necessary qualifications insisted in the cases Paul and the Twelve. It may be difficult always to decide in which sense an individual is designated an apostle. Notice the cases of Apollos, Barnabas, James, Jude, and Silas. Yet this difficulty ought not to cloud the basic clarity of this distinction. That there is a line between big A and small a apostles is clear. we simply do not have enough information to decide on which side of the line some `apostles' fall.

2. It cannot be denied that there is some flexibility with regard even to the Big A-apostles. The apostolate is not rigidly restricted to the Twelve alone. (38) The instances of Paul and James establish this. Also, interesting in this regard is the possibility that Paul's intimate associates obtained a kind of apostolicity from him.

3. We must, however, insist on the strict limits of the narrower Apostolate. The qualities of eye-witness; direct, divine appointment; and supernatural powers are absolute necessities to claim an apostolate like that of the Twelve and Paul. These unique qualities point us to the unique, un-repeatable, historically limited identity of the Apostolate. The idealized or symbolic references of the New Testament to the
Apostolate (Matt. 16:17; 19:28; Eph. 2:20; Rev. 21:14) likewise suggest, the "closed character" or the "limited identity" of the Apostolate."

Sam Waldron