Many people from mainstream religions are surprised at the high rate at which  Alternative Religions are proliferating and growing everywhere. This numerical growth does not result automatically.  Rather it is because the new religions offer something that others are not able to give.
They Offer Something For The Prevailing  Spiritual Vacuum: As mainstream religions grow and reach a certain critical mass, most of  them  tend to become fixed in their beliefs and in what they offer. While this would be sufficient for the generation in which the mainstream religion developed and prospered,  often this is insufficient to meet the needs of newer followers. Alternative Religions are small and vibrant groups that can easily meet these needs, and thus they attract plenty of followers.
Sacrificial Giving: All Alternative Reiligions encourage sacrificial giving for charity and for spreading the faith. This in turn helps them to send out  a large trained manpower who would invite others to this group persuasively.
They Often Have A Massive Print-media Setup:  Alternative Religions produce large amounts of illustrated and persuasively written material to bring information, comfort and encouragement to inquirers and followers alike. They touch upon every aspect of life so that the follower gets everything he needs to from the group itself.
They Effectively Use Mass Media: Though Mass Media can never take the place of personal contact, it can create a vast pool of faithful listeners: This in turn provides a very large number of people ready for personal contact and eventual absorption into the Alternative Religion. Most Alternative Religions use all available media for this purpose.
Every Member Is A Persuader:  Most Alternative Religions emphasize that working as a missionary is an essential and compulsory part of the individual's  spiritual obligation.  This strategy makes everyone a persuader -- a missionary manpower which traditional religions cannot match. Eventually this manpower takes the new religion to a point from where it starts enjoying sudden and very large (geometrical) growth. This is one way in which many Alternative Religions are growing very rapidly today. 
They Have Numerous Institutions: Academic and social service institutions offer great opportunities for Alternative Religions to grow and multiply. Both of the above types of establishments can help them to help train and empower  people, and also to offer jobs to new folowers. The centralized administration ensures the availability of resources, technical guidance, and all needed legal help.
They Offer Friendship And Fellowship: People struggling for answers need help not only orally but also practically. The Alternative Religions know this very well and they offer a good deal of personal attention to prospective members and also to the new disciples. By the time these followers  mature, they would change from care-receivers to care-givers, maintaining a continuity of personal relationship. Almost all  Alternative Religions exhibit this close-knit family relationship, making them very attractive. 
They Are Sensitive To Human Needs: Every person has needs, and more so when he is passing through the "struggle" stage of life. Further, the range and intensity of such needs have become great today because of the changing society and breaking families. Alternative Religions are quite sensitive to these needs of people and offer many kinds of help. 
In summary, the Alternative Religions are able to offer something that people need immdiatly, and which traditional religions are not able to offer.