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Search by keyword all the groups in linked in. The software will create a list with the group name, the group url and the number of members. You can sort the list by the groups that contain more members, then join the groups and contact the members to offer your products or services. It also extract companies by keywords.
Load a list of the groups where you want to join, then let the software join to them for you. Once you join to the groups you will be able to comment on them and extract the members in the group so you could offer them services or offers.
Type the url of the group in linked that you have joined, then get a list of the members that are inside that group so you can contact them or ask for connection and promote your service or product to them. This is awesome cause you will find people already interested in your niche since they are already in a group for that niche. They will be more likely to buy from you.