I read stories in Petavatthu which describe how people offer donations to the sangha and transfer the merit to their deceased relatives who are born as hungry ghosts, so that they can get alleviate the suffering experienced by the hungry ghosts. In the same way, is it possible to share merit to other beings like Angels, animals, etc, because I haven't come across this in the texts.
Not sure Dhammadhatu's answer is direct answer for this question.
So sharing merit (telling your good merit) to animals doesn't work because they (almost every of animals) do not have any mind to understand good merit and eventually not able to be happy/together with you about your merit. So they will not share the effect of being happy/together of good merit.
Angles (frequently gods in Buddhist literature) may have little chance to know/care about your good merit since their lives are more about consuming the effects of good karma instead of cultivating good karma and sharing merit of others. There might possibility that some lower angels (gods) wandering on earth or living like human among us who can be shared our good merit but it is not so strong effects like on hungry ghosts because it is greatly differ in terms of necessity.
Traditionally, the amount of merit you could send to an "angel" (I'm assuming this is a translation of "deva?" Caroline Rhys Davids used to translate "deva" as "angel.") is incredibly meagre compared to the amount they already have. This is not your or "our" fault. We are humans who live here because of certain past deeds. A human birth is precious, but a divine birth is more pleasurable and is the fruit of greater merit.
We send merit to the ghosts, animals, demons, because they are destitute in spiritual poverty. They "need" it, so to speak. There is nothing at all stopping you from transferring merit to the gods, but they don't "need" it in a way those suffering in the lower destinies do.
If you want to help the ghosts, get wholesome food and drink in seven clean vessels each, an excessive amount is not necessary. Seven vessels of pure water and seven vessels of vegetables would do nicely. Meat is not "wholesome food" for this exercise. As much as you would eat. You won't be eating the food if you do this, so keep that in mind.
Place the food and drink on your altar. Perform loving-kindness meditation to sentient beings in all directions. Then, recollect the sufferings of the hungry ghosts and send maitrī to those of the unfortunate destinies. Assume the dhyānamudrā. Recite in a strong clear moderately-loud voice (your pronunciation doesn't matter too much for this kind of lay ceremony):
唵啞葛嚕穆看薩哩斡塔哩麻南啞牒耶奴忒班荅奴忒 on akaro mokan sariwa tо̄rimanan achōyadoto hantōdoto
唵啞吽癹吒莎訶 on a un ho sоwaka
This dhāraṇī requires no empowerment or ordination. This is a section of the "Releasing of the Flaming Mouths," a food offering with a mantra. A more "souped-up" version of this is performed by the saṁgha for funerals. The food will be able to satiate the hungry ghosts. It is said that upon eating the food, the ghosts will become freed of ghosthood and be reborn as animals or humans according to their karma. Afterward, leave the food in the woods or burn it. Do not eat it. The vessels can be washed and re-used for anything. It is recommended to very thoroughly wash them.