"We need to stop running to the hills in white robes, but do everything we can to tell the world about Christ before He returns," Dr Youssef told more than 1,000 people at Westminster Chapel.
His message at the event, hosted by Premier Christian Radio, was inspired by Luke 19 where Jesus says 'Occupy till I come'.
Instead of trying to predict the date and time of Christ's return, Dr Youssef instead suggested that Christians get on with serving others.
"Just seeing the urgency of the time should not just make us sit there and count the days but really get busy witnessing and serving and getting involved in global evangelism, which is what Leading The Way does," he said.
"We need to get busy, serve God, lift Jesus up, don't be intimidated or be fearful. Let the word do it as Martin Luther says you lift up Jesus and He'll do the rest."
Although based in America, Dr Youssef is originally from Egypt and has just recently started broadcasting his ministry's satellite TV channel to the Arab world.
"If you told me four years ago that we would have a television station broadcasting 24/7 into 160 million homes in the Arab world and Europe on Arab sat and Nile sat the most popular Arab satellites I wouldn't have believed it. But God really put it together," he said.
Premier presenter Muyiwa said it was a very significant time for Dr Youssef to be in London.
"I think it's a great thing to have the unadulterated word of God spoken in London. There's something about a significant leader like Dr Youssef coming in that makes a difference to a whole city . I think Michael is definitely someone who has a voice and a message for not just the church but for the city and the nation," he said.
Many people responded at the end of the night as he urged them to take their calling as ambassadors of Christ seriously.
Dr Youssef added: "I believe that if the believers unite together in prayer and commitment we could see a great revival. I tell people if the Lord returns today He's not going to find me in a white robe heading to the hills or sitting in the mountains.
"He's going to find me either behind a pulpit, or behind a desk or behind a microphone in a studio or with somebody ministering and that's what should really be our attitude.
"I think it was John Wesley who said 'I wait for the Lord everyday but I work as if He's not coming back for a thousand years."