VJs are mainly employed by Music channels, Producers of music shows and film based programmes. 

Besides popular prospective employers like MTV, Channel V, B4U music, MCM Asia etc, there are many number of channels including regional ones who are in demand of VJ's. But it is not easy to get a break in the field. You may be employed on a contract basis per show or on a full time basis. There will be paper adds calling VJ's or VJ hunts advertised on TV. The selection will be tough, which may include a test on paper, on voice modulation or facing the camera. Your screen presence, physique and voice, and ability to stand out in the crowd will go a long way in being selected. 

Once you are selected, there is no such thing as hierarchy in this profession.  Beginners with talent may get to handle their own shows within the first 6 months. It mainly depends on your ability. Besides the excellent pay, you get to host shows in the country or abroad, meet celebrities, and be on the glam walk of life. Keeping up the popularity for long is not easy and as such this profession is a short lived one. The rule is make hay while it lasts. But the profession gives you ample scope to diversify to various fields such as Modeling, Theatre (direction/acting), Film (acting), Music videos (directing/acting/choreography), Anchoring, News casting, PR etc. that generally VJ's do. The more popular you get through veejaying the more the choices you may have.