God is not limited, and He is certainly able to work in miraculous ways today just as He did in biblical times, if He so chooses. If He didn't, why would we bother to pray when a loved one falls ill or God's work is opposed by evil forces?
At the same time, much of what God does in the world is hidden from us. Think, for example, of the work He has given His angels to do on our behalf. Occasionally they may make their presence known, but for the most part, they're hidden from us, and only in heaven will we understand how they protected us or delivered us from danger. Much of what they do could be labeled as miracles. The Bible says, "Are not all angels ministering spirits sent to serve those who will inherit salvation?" (Hebrews 1:14).
Would more people believe in God or in Christ if they saw a miracle? Not necessarily. Countless people saw Jesus perform miracles, yet they refused to believe in Him or give their lives to Him. Don't let this be true of you!
The greatest miracle of all, however, is the miracle of a changed life -- and this can happen, as we open our hearts and lives to Christ. Do others see Christ in you -- His love, His compassion, His purity, His joy? Make sure of your commitment to Christ, then ask Him to change you from within by His Holy Spirit, and make you a living witness to the miracle of His transforming power.