Is it obligatory to seek out people who were wronged in the past to ask for their forgiveness, knowing that the wrongdoing was only verbal, and is it sufficient to be good to them now instead of explicitly asking for forgiveness?

You must seek forgiveness from anyone you have wronged, whether verbally or otherwise, as long as you were an adult and of sound mind at the time of the wrongdoing. Simply being kind to them now is not enough. If you are unable to reach them, or fear that seeking their forgiveness would lead to a greater harm, then supplicate for them and seek Allah's forgiveness for them.