When we send the energy of love and compassion to another person, it doesn't matter if they know we are sending it.  The important thing is that the energy is there and the heart of love is there and is being sent out into the world.  When love and compassion are present in us, and we send them outward, then that is truly prayer.
In prayer there has to be mindfulness, concentration, insight, loving kindness, and compassion to put electric current in the wire.  We have to pray with our body, speech, and mind and with our daily life.  With mindfulness, our body, speech and mind can become one.
When we begin to pray, we may not yet be good at it, but we will already be able to generate some energy.  Gradually, as we begin to practice the precepts, concentration, and insight, our prayers will have more force, more power.
When the energies of compassion, understanding, and mindfulness are present, wisdom is more likely to arise.  We do not change ourselves alone, but we change the collective consciousness.  That collective consciousness is the key to all change.
We don't need to send prayers anywhere, because God is omnipresent.  Prayer is unlimited by space or time.
If there is a change in the individual consciousness, then a change in the collective consciousness will also take place.  When there is a change in the collective consciousness, then the situation of the individual can change; the situation of our loved one who is the object of our prayer can change.  This is why Buddhists say that everything arises from the mind.  Our mind is a creation of the collective consciousness.  If we want to have change, we have to return to our mind.  Our mind is a center that produces energy.  From this powerhouse we call mind, we can change the world.  We change it by means of a rel energy that we ourselves have created.  This is the most effective way of prayer.
In the Buddhist tradition, we know that praying as a community, a Sangha, is stronger than praying as an individual.  When we simultaneously practice sending spiritual energy, then that energy is magnified and much more effective.
We pray, but sometimes we may have a situation that is very difficult and we need a stronger energy.  The individual energy we can send is already something, but if we have a Sangha that is free and solid then the energy we can send together will certainly be greater.  Our own undivided attention is a key to open the door of the ultimate reality and the undivided attention of our friends in the pravtice is an even greater key.  When a Sangha of one hundred or one thousand people practices purifying the actions of body, speech, and mind, and unifying body and mind to send energy, the energy generated will be very powerful, and will be able to change the situation which we call karma, the causes and effects of our actions.
In Buddhism, we know that the one we are praying to lies inside as well as outside of us.