Increased or have increased

both are correct, but 2) sounds better...

Are you still looking for an inrease/decrease or is the increase period over.

Simple past vs past perfect. Its your choice.

Both are correct but 2 is made for dummies...redundant!

In 2016, they increased. In the past year they have increased.

Speakers of American English generally use the present perfect tense (have/has + past participle) far less than speakers of British English. In spoken American English, it is very common to use the simple past tense as an alternative in situations where the present perfect would usually have been used in British English. The two situations where this is especially likely are:

1. In sentences which talk about an action in the past that has an effect in the present. One common significance of the present perfect is to refer to a resulting state in the present of some action in the past, e.g. the profits of a company over the year which ends in the present.

2. In sentences which contain the words already, just or yet.