Hebrews Chapter 1 verse 14 says, using the New American Translation of the Bible, " Are they not all ministering spirits, sent out to render service for the sake of those who will inherit salvation?
As clear as this verse is, the idea of asking for an angel or the help of an angel for anything specific does seem to be underplayed. For sure, upping the ante a bit with personal prayer has to be to a degree self reliant and between you and the Lord. No third party need be privy to your percise prayer discussions with the Lord. However this mode of self reliance doesn't preclude angels and for all matters practical angels are there.
While angels often assist behind the scenes, it might be that an angel will appear to you in the appearance of a man or women, and this itself is significant in that the demeanor of the angel, what the angel says how the angel says it is something to make note of and think about.
Although the angel might have an appearance quite similar to other people in the area the angel will often have a stand out appearance, maybe immaculately dressed and so on.
How the angel comes into your space or leaves your space will be enough to let you know that you have just dealt with an angel, if you are alert to it.
It is certainly not necessary that you see the angel and at times you might just see the work of the angel, or what the angel does. In other cases you might not know or see that the angel has done but the help still occurred.
It might not be any ongoing problem where you would ask for the assistance of an angel, it could also be a situation where you are anticipating that you might have a problem, like walking in a new city while waiting for the train transfer and asking for an angel to help you in this specific time frame and location. The appearance of the angel in this case as in response for your specific request for an angel is confirmation that you should indeed be requesting the help of angels in the matter of specifics, and these request go right to the present, it is not a down the road type thing. The angel is here to help right now, right here, or at least today if the situation you are facing is to be today.
If the angel does appear to you in the form of a person, this is for your encouragement and the actions of the angel will be along the lines of the specific encouragement you need, it might be as simple as reassure that the angel is around, close by and here to help.