I've playing a couple years now and having been trying to play with a metronome in order to work on speed/accuracy. The problem I've been having is that I can't really "lock in" to the rhythm and play to that beat. The thing I've noticed is that if I practice or improvise to a backing track, it's much easier to get the rhythm and play in time with the song, even on faster pieces of music.

I'd love it if anyone had advice for being able to do things such as 16th notes to the click.
tap your foot, may sound simple but it helped me so much! just tapping your foot and keeping in beat with the metronome will keep your body in with the beat and it'll flow through you a lot easier. If you're still having problems with keeping on the beat, practice with just hitting the first beat of the bar and the rest will fall into place!
You could also try using a drum machine. There are some really cheap (maybe even free) apps out there you could try, or do a quick google search for "online drum machine" or "virtual drum machine" and see what pops up. Most of those will let you adjust tempo. I generally find it easier to lock in with a full drum groove, rather than a simple metronome click.
drum grooves are not a substitute for metronomes. The point of a metronome is that YOU produce the rhythm, not the click. The click is just the tempo.

It sounds like the OP here needs to bone up on the basics of rhythm: time signatures, counting, note values, etc. I think once you know what different note values are supposed to sound like you'll have a much easier time making them with the metronome and with actual music.
Quote by cdgraves
drum grooves are not a substitute for metronomes.

I would have to disagree with this point. If the overall goal is to achieve a better sense of pulse, I have found that drum grooves can really help internalize pulse.

Of course the ultimate goal is to be able to develop your own sense of rhythm, but drum grooves can be a great means to that end.