Erik Raymond shares a story that will encourage you to not give up in sharing the gospel. Read Evangelism is Fueled by Knowing God is at Work which ends with this exhortation:
In our Christian lives, and in evangelism in particular, our job is to be faithful. This faithfulness corresponds with how we represent Christ. Our faithfulness does not depend upon the amount of God’s apparent blessing of what we are doing. In other words, if people are not getting converted it does not mean that we tame it down. It is true that we have no idea what God is doing in the small things but we do know what he is ultimately doing: God is doing all things for his glory. And we know how he does it: He does it through means, even the faithfulness of his people.
If you are discouraged, and even weary in the work of evangelism, then consider this true story. And then, remember this: God uses the faithfulness of his people to glorify his name.
In one sense you have no idea what God is doing. And in another sense, you know exactly what he is doing. Therefore, trust him and keep being faithful.