I want to start trading in Bitcoin to dollar,
but I looking for someone sends me mesages
every day tells me it's time to buy and it's time to sell.
Where can I find this person? 
If you want to be successful in trading then this kind of state is inappropriate. You shouldn't be needing a person to remind you when to sell and when to buy, you should know it yourself. It's your money at stake so do not entirely trust it to other peoples opinion or whatsoever.
Rather than looking for this person study more about Bitcoin and do more research on it you yourself will be in a state to guide others about when to buy and when to sell bitcoins.